Display device

ABSTRACT

To provide a display device with low power consumption. The display device includes a plurality of pixels each having a light-emitting element having a structure in which light emitted from a light-emitting layer is resonated between a reflective electrode and a light-transmitting electrode, wherein no color filter layers are provided or color filter layers with high transmittance are provided in pixels for light with relatively short wavelengths (e.g., pixels for blue and/or green), and a color filter layer is selectively provided in pixels for light with a long wavelength (e.g., pixels for red), and thereby maintaining color reproducibility and consuming less power.

This application is a continuation of copending U.S. application Ser.No. 14/873,938, filed on Oct. 2, 2015 which is a continuation of U.S.application Ser. No. 13/410,799, filed on Mar. 2, 2012 (now U.S. Pat.No. 9,153,627 issued Oct. 6, 2015), which are all incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the present invention relates to anelectroluminescence display device and a manufacturing method of thedisplay device.

2. Description of the Related Art

In recent years, as display devices (so-called flat panel displays)which are very thin and light, electroluminescence (hereinafter, alsoreferred to as EL) display devices have been attracting attentions.

As a multicolor display method of an EL display device, there isproposed a method in which a light-emitting element for white light anda color filter are combined (see, for example, Patent Document 1). Inthis method, it has been thought that it is not necessary to separatelyform light-emitting elements using light-emitting materials fordifferent emission colors in every pixel, and thus high definition canbe achieved.

However, when a color filter is used, light other than light in aparticular wavelength band is absorbed by the color filter, so thatthere is a loss of light and light emitted from a light-emitting elementcannot be used effectively. For this reason, in order to obtain adesired luminance sufficiently, a loss of light needs to be compensatedby an increase in luminance of the light-emitting element, which resultsin an increase in power consumption unfortunately.

REFERENCE

[Patent Document 1] Japanese Published Patent Application No. H07-220871

SUMMARY OF THE INVENTION

In view of the above, it is an object of one embodiment to decreasepower consumption of an EL display device for multicolor display.

One embodiment of the present invention includes a plurality of pixelseach including a light-emitting element having a structure of resonatinglight emitted from a light-emitting layer, between a reflectiveelectrode and a light-transmitting electrode. In a pixel of an emissioncolor with a relatively short wavelength (for example, a pixel for bluelight and/or a pixel for green light), a color filter layer is notprovided or a color filter layer having a high transmittance isprovided, and in a pixel of an emission color with a long wavelength(for example, a pixel for red light), a color filter layer isselectively provided, so that a display device having high colorreproducibility and low power consumption can be provided. In addition,a plurality of light-emitting elements in each pixel have a commonstructure between pixels, without being formed separately. In thismanner, a display device with high definition can be provided.Specifically, the following structure can be employed, for example.

One embodiment of the present invention is a display device comprising afirst substrate provided with a first light-emitting element, a secondlight-emitting element, and a third light-emitting element; and a secondsubstrate including a first region overlapping with the firstlight-emitting element, a second region overlapping with the secondlight-emitting element, a third region overlapping with the thirdlight-emitting element, and a color filter layer at least in the thirdregion. In the display device, the first light-emitting elementincludes, between a first reflective electrode and a light-transmittingelectrode, a first light-emitting layer having a maximum emission peakin a blue wavelength region, a second light-emitting layer having amaximum emission peak in a green wavelength region, and a thirdlight-emitting layer having a maximum emission peak in a red wavelengthregion, and light emitted from the first light-emitting layer isresonated between the first reflective electrode and thelight-transmitting electrode; the second light-emitting element includesthe first light-emitting layer, the second light-emitting layer, and thethird light-emitting layer between a second reflective electrode and thelight-transmitting electrode, and light emitted from the secondlight-emitting layer is resonated between the second reflectiveelectrode and the light-transmitting electrode; and the thirdlight-emitting element includes the first light-emitting layer, thesecond light-emitting layer, and the third light-emitting layer betweena third reflective electrode and the light-transmitting electrode, andlight emitted from the third light-emitting layer is resonated betweenthe third reflective electrode and the light-transmitting electrode; thefirst region has a maximum transmittance of 80% or more in the bluewavelength region, the second region has a maximum transmittance of 75%or more in the green wavelength region, and the color filter layer inthe third region has a transmission center wavelength in the redwavelength region.

In the display device, a color filter layer having a transmission centerwavelength in the green wavelength region may be provided in the secondregion.

In the display device, the color filter layer provided in the secondregion may have a maximum transmittance of 10% or more in a wavelengthregion of from 380 nm to 450 nm, inclusive.

In the display device, a color filter layer having a transmission centerwavelength in the blue wavelength region may be provided in the firstregion.

In the display device, the color filter layer provided in the firstregion may have a maximum transmission of 5% or more in a wavelengthregion of from 570 nm to 760 nm, inclusive.

In the display device, the second light-emitting element may include afirst light-transmitting conductive layer so as to be in contact withthe second reflective electrode, and the third light-emitting elementmay include a second light-transmitting conductive layer having athickness different from that of the first light-transmitting conductivelayer, so as to be in contact with the third reflective electrode.

In the display device, the area of the first region is preferablysmaller than that of the third region.

In accordance with one embodiment of the present invention, a displaydevice that achieves low power consumption can be provided.

Further, in accordance with one embodiment of the present invention, adisplay device with high color reproducibility can be provided.

Accordingly, in accordance with one embodiment of the present invention,a display device with high definition can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B each illustrate a display device in accordance with oneembodiment of the present invention;

FIG. 2 illustrates a light-emitting element which can be applied to oneembodiment of the present invention;

FIGS. 3A to 3C each illustrate a light-emitting element in accordancewith one embodiment of the present invention;

FIGS. 4A and 4B illustrate a display device in accordance with oneembodiment of the present invention;

FIGS. 5A to 5D are diagrams showing a display device in accordance withone embodiment of the present invention;

FIGS. 6A to 6C each illustrate an example of a usage mode of a displaydevice;

FIG. 7 illustrates an element structure of Example 1;

FIG. 8 is a graph showing characteristics of the display device ofExample 1;

FIG. 9 is a graph showing characteristics of the display device ofExample 1;

FIG. 10 is a graph showing transmittances of color filter layers;

FIG. 11 is a graph showing transmittances of color filter layers; and

FIGS. 12A and 12B are graphs each showing characteristics of a displaydevice of Example 2.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described with reference to the drawings. However,the present invention is not limited to the following description, andvarious changes for the modes and details thereof will be apparent tothose skilled in the art unless such changes depart from the spirit andthe scope of the invention. Therefore, the present invention is notconstrued as being limited to description of the embodiments. In thestructures to be given below, the same portions or portions havingsimilar functions are denoted by the same reference numerals indifferent drawings, and explanation thereof will not be repeated in somecases.

Note that in this specification and the like, the terms of ordinalnumbers such as the first to the N-th (N is a natural number) are usedconveniently for preventing confusion between components, and thus donot limit a process order or a stack order numerically. In addition, theordinal numbers in this specification do not denote particular nameswhich specify the present invention.

Embodiment 1

A display device in this embodiment includes a first substrate that isprovided with a first light-emitting element, a second light-emittingelement, and a third light-emitting element; a first region (included ina first pixel) overlapping with the first light-emitting element andsandwiched between the first light-emitting element and a secondsubstrate; a second region (included in a second pixel) overlapping withthe second light-emitting element and sandwiched between the secondlight-emitting element and the second substrate; a third region(included in a third pixel) overlapping with the third light-emittingelement and sandwiched between the third light-emitting element and thesecond substrate; and a second substrate that is provided with a colorfilter layer in at least the third region.

The first light-emitting element includes, between a first reflectiveelectrode and a light-transmitting electrode, a first light-emittinglayer having a maximum emission peak in a blue wavelength region, asecond light-emitting layer having a maximum emission peak in a greenwavelength region, and a third light-emitting layer having a maximumemission peak in a red wavelength region, and light emitted from thefirst light-emitting layer is resonated between the first reflectiveelectrode and the light-transmitting electrode. In addition, the secondlight-emitting element includes, between a second reflective electrodeand the light-transmitting electrode, the first light-emitting layer,the second light-emitting layer, and the third light-emitting layer, andlight emitted from the second light-emitting layer is resonated betweenthe second reflective electrode and the light-transmitting electrode. Inaddition, the third light-emitting element includes, between a thirdreflective electrode and the light-transmitting electrode, the firstlight-emitting layer, the second light-emitting layer, and the thirdlight-emitting layer, and light emitted from the third light-emittinglayer is resonated between the third reflective electrode and thelight-transmitting electrode.

The display device in this embodiment has the maximum transmittance inthe blue wavelength region of 80% or more in the first region (includedin the first pixel), the maximum transmittance in the green wavelengthregion of 75% or more in the second region (included in the secondpixel), and the color filter layer provided in the third region(included in the third pixel) has a transmission center wavelength inthe red wavelength region.

One specific embodiment of an EL display device will be described belowwith reference to FIGS. 1A and 1B, FIG. 2, and FIGS. 3A to 3C.

FIG. 1A illustrates a structural example of a cross-sectional view of adisplay portion in the display device in this embodiment.

The display device illustrated in FIG. 1A includes a first pixel 130 a,a second pixel 130 b, and a third pixel 130 c. The first pixel 130 aincludes a first light-emitting element 132 a provided over a substrate100. A second pixel 130 b includes a second light-emitting element 132 bprovided over the substrate 100. A third pixel 130 c includes a thirdlight-emitting element 132 c provided over the substrate 100, and acolor filter layer 134 c provided in a region overlapping with the thirdlight-emitting element 132 c, in a counter substrate 128.

The first light-emitting element 132 a, the second light-emittingelement 132 b, and the third light-emitting element 132 c include afirst reflective electrode 102 a, a second reflective electrode 102 b,and a third reflective electrode 102 c, respectively, which are disposedseparately from each other over the substrate 100. In addition, thefirst light-emitting element 132 a, the second light-emitting element132 b, and the third light-emitting element 132 c are electricallyinsulated from each other by an insulating layer 126.

The insulating layer 126 is formed using an organic insulating materialsuch as polyimide, acrylic, polyamide, or epoxy, or an inorganicinsulating material. Preferably, the insulating layer 126 is formedusing a photosensitive resin material, in particular, in such a way thatan opening is formed over the reflective electrode and a sidewall of theopening has an inclined surface with continuous curvature. Theinsulating layer 126 may be tapered or inversely tapered.

The first light-emitting element 132 a includes an EL layer between thefirst reflective electrode 102 a and a light-transmitting electrode 112.The EL layer includes at least the first light-emitting layer having amaximum emission peak in a blue wavelength region, the secondlight-emitting layer having a maximum emission peak in a greenwavelength region, and the third light-emitting layer having a maximumemission peak in a red wavelength region. In addition, the EL layer canhave a stacked-layer structure including a hole-injection layer, ahole-transport layer, an electron-transport layer, an electron-injectionlayer, and/or the like, in addition to the first to third light-emittinglayers. In addition, a plurality of EL layers may be stacked and acharge-generation layer may be provided between one EL layer and anotherEL layer.

Note that in this specification and the like, specifically, the bluewavelength region means a wavelength region of from 430 nm to 470 nm,the green wavelength region means a wavelength region of from 500 nm to550 nm, and the red wavelength region means a wavelength region of from600 nm to 700 nm.

In addition, the second light-emitting element 132 b includes an ELlayer between the second reflective electrode 102 b and thelight-transmitting electrode 112, the third light-emitting element 132 cincludes an EL layer between the third reflective electrode 102 c andthe light-transmitting electrode 112. The EL layers included in thesecond light-emitting element 132 b and the third light-emitting element132 c are common to that of the first light-emitting element 132 a, andthe EL layers are continuous (i.e., a continuous layer) between thefirst light-emitting element 132 a, the second light-emitting element132 b, and the third light-emitting element 132 c. Note that lightemitted from the first light-emitting element 132 a, the secondlight-emitting element 132 b, and the third light-emitting element 132 care output through the light-transmitting electrode 112.

In this embodiment, between the electrodes having reflectivity (thefirst reflective electrode 102 a, the second reflective electrode 102 b,and the third reflective electrode 102 c) and the light-transmittingelectrode 112, a first EL layer 106 including the first light-emittinglayer, a charge-generation layer 108, and a second EL layer 110including the second light-emitting layer and the third light-emittinglayer are sequentially stacked. Note that one embodiment of the presentinvention can employ a light-emitting element with this structure, butis not limited to, and for example, the stack order of the firstlight-emitting layer, the second light-emitting layer, and the thirdlight-emitting layer can be changed.

In the first light-emitting element 132 a, the second light-emittingelement 132 b and the third light-emitting element 132 c, the first ELlayer 106, the charge-generation layer 108, and the second EL layer 110are each a common layer and continuous between pixels. Accordingly, inthe manufacturing process, the layers are not necessarily formed withuse of a metal mask, and thus a film can be formed over a large area,which can allow the display device to be enlarged and formed with highproductivity. Further, a display region can be enlarged in a displayportion. Furthermore, defects generated due to entry of particles inusing a metal mask can be prevented, and thereby a display device can bemanufactured with high yield.

In addition, the first light-emitting element 132 a, the secondlight-emitting element 132 b, and the third light-emitting element 132 cinclude a first light-transmitting conductive layer 104 a, a secondlight-transmitting conductive layer 104 b, and a thirdlight-transmitting conductive layer 104 c, respectively, which have adifferent thickness from each other, and thereby the elements 132 a, 132b, and 132 c also have different thicknesses.

The film thickness of the first light-transmitting conductive layer 104a provided in the first light-emitting element 132 a is controlled, sothat an optical path length can be adjusted to resonate light (lightwith a maximum emission peak in the blue wavelength region) emitted fromthe first light-emitting layer to be intensified between the firstreflective electrode 102 a and the light-transmitting electrode 112.

The film thickness of the second light-transmitting conductive layer 104b provided in the second light-emitting element 132 b is controlled, sothat an optical path length can be adjusted to resonate light (lightwith a maximum emission peak in the green wavelength region) emittedfrom the second light-emitting layer to be intensified between thesecond reflective electrode 102 b and the light-transmitting electrode112.

The film thickness of the third light-transmitting conductive layer 104c provided in the third light-emitting element 132 c is controlled, sothat an optical path length can be adjusted to resonate light (lightwith a maximum emission peak in the red wavelength region) emitted fromthe third light-emitting layer to be intensified between the thirdreflective electrode 102 c and the light-transmitting electrode 112.

By the adjustment of each optical path length so as to resonate lightemitted from each light-emitting layer to be intensified, such resonatedlight can exhibit a higher front luminance in the case where the sameamount of current is applied. Therefore, the emission efficiency of eachlight-emitting element can be increased. In addition, by selectivelyamplifying light of each wavelength region, a light-emitting elementwith higher color purity can be provided.

For example, the film thickness of the light-transmitting conductivelayer 104 (the first light-transmitting conductive layer 104 a, thesecond light-transmitting conductive layer 104 b, or the thirdlight-transmitting conductive layer 104 c) may be controlled so that theoptical path length between the reflective electrode 102 (the firstreflective electrode 102 a, the second reflective electrode 102 b, andthe third reflective electrode 102 c) and the light-transmittingelectrode 112 can be (2n−1)/4 times (n is a natural number) a desiredwavelength.

Note that when a functional layer is provided for the first EL layer 106or the like, the optical path length between the first reflectiveelectrode 102 a and the light-transmitting electrode 112 may be adjustedby controlling the film thickness of the functional layer. In this case,the first light-transmitting conductive layer 104 a is not necessarilyprovided.

In the display device illustrated in FIG. 1A, the first light-emittingelement 132 a included in the first pixel 130 a is an element withimproved blue color purity by an optical resonant structure (so-calledmicro cavity structure). The blue wavelength region lies in a shortwavelength of from 430 nm to 470 nm, and thus the resonant wavelength inthe first light-emitting element 132 a is also short, as a result,colors other than blue are hardly mixed. Accordingly, the first pixel130 a can exhibit good blue chromaticity even when no color filter layeris provided for the first pixel 130 a. Therefore, light absorption thatmight occur when a color filter layer is provided for the first pixel130 a can be eliminated, which can lead to improvement in use efficiencyof light.

In addition, the second light-emitting element 132 b included in thesecond pixel 130 b is an element with improved green color purity by anoptical resonant structure (so-called micro cavity structure). The greenwavelength region lies in a relatively short wavelength of from 500 nmto 550 nm, and thus the second pixel 130 b can exhibit good greenchromaticity even when no color filter layer is provided for the secondpixel 130 b either. Therefore, light absorption that might occur when acolor filter layer is provided for the second pixel 130 b can beeliminated, which can lead to improvement in use efficiency of light.

Also, the third light-emitting element 132 c included in the third pixel130 c is an element with improved red color purity by an opticalresonant structure (so-called micro cavity structure). However, the redwavelength region lies in a long wavelength region of from 600 nm to 700nm, and thus in the third light-emitting element 132 c, the resonantwavelength of light exhibiting red color is close to the resonantwavelength of light with a short wavelength (light exhibiting blue coloror the like) and causes a mixed color in some cases. For example,because a 1 wavelength of light exhibiting red color matches a 3/2wavelength of light exhibiting blue color, if an optical design is setto resonate light with a wavelength of 600 nm, light with a wavelengthof 400 nm may also be resonated. For this reason, the color filter layer134 c is preferably provided for the third pixel 130 c.

Note that it is preferable that the color filter layer 134 c has atransmission center wavelength in the red wavelength region (forexample, the transmission center wavelength is 690 nm), because lightemitted from the third light-emitting element 132 c can be outputefficiently.

In this specification, the “transmission center wavelength” means acenter wavelength of the wavelength region (preferably, a wavelengthregion with transmittance of 50% or more) of light transmitted through acolor filter layer in the visible light region (380 nm to 780 nm). Forexample, when the wavelength region of light transmitted through a colorfilter layer having a transmission center wavelength in the bluewavelength region is 380 nm to 520 nm, the transmission centerwavelength is 450 nm; when the wavelength region of light transmittedthrough a color filter layer having a transmission center wavelength inthe green wavelength region is 510 nm to 590 nm, the transmission centerwavelength is 550 nm; and when the wavelength region of lighttransmitted through a color filter layer having a transmission centerwavelength in the red wavelength region is 600 nm to 780 nm, thetransmission center wavelength is 690 nm.

As the color filter layer 134 c, for example, a chromaticlight-transmitting resin can be used. As such a chromaticlight-transmitting resin, a photosensitive organic resin or anonphoptosensitive organic resin can be used. A photosensitive organicresin layer is preferable, because the number of resist masks can bedecreased, leading to simplification of a process.

Chromatic colors are colors except achromatic colors such as black,gray, and white. A color filter layer is made of a material whichtransmits only the chromatic color light that is colored. As chromaticcolor, red, green, blue, or the like can be used. Alternatively, cyan,magenta, yellow, or the like may also be used. “Transmitting only thechromatic-color light that is colored” means that the light transmittedthrough the color filter layer has a peak at a wavelength of thechromatic-color light.

This embodiment describes the example in which the color filter layer134 c is provided on the inner side of the counter substrate 128, butthe present invention is not limited to the example, and the colorfilter layer 134 c can be provided on the outer side of the countersubstrate 128 (the side opposite to the light-emitting element).Alternatively, over the third light-emitting element 132 c, a chromaticlight-transmitting resin serving as a color filter layer may be formed.

As illustrated in FIG. 1A, the first pixel 130 a for blue (B) and thesecond pixel 130 b for green (G) are not provided with a color filterlayer, while the third pixel 130 c for red (R) is selectively providedwith the color filter layer 134 c. By this structure, lower powerconsumption of a display device can be achieved, keeping high colorreproducibility and high national television standards committee (NTSC)ratio.

As described above, the first light-emitting element 132 a provided inthe first pixel 130 a hardly mixes colors other than blue, and thus canprovide higher use efficiency of light than the third light-emittingelement 132 c provided in the third pixel 130 c. Therefore, even whenthe area of the first pixel 130 a is made smaller than that of the thirdpixel 130 c, sufficient color reproducibility can be achieved. Forexample, when the light use efficiency of the first light-emittingelement 132 a is four times that of the third light-emitting element 132c, the area of the first pixel 130 a can be ¼ to ⅓ of that of the thirdpixel 130 c. The first pixel 130 a has no color filter layer; therefore,the area of the first pixel 130 a is made small, thereby reducingreflection of external light by the first reflective electrode 102 a ona display surface. Thus, the contrast of the display device can beincreased.

In addition, in the display device illustrated in FIG. 1A, alight-blocking layer may be provided in a region overlapping with theinsulating layer 126. The light-blocking layer is formed using alight-blocking material that reflects or absorbs light. For example, ablack organic resin can be used, which can be formed by mixing a blackresin of a pigment material, carbon black, titanium black, or the likeinto a resin material such as photosensitive or non-photosensitivepolyimide. Alternatively, a light-blocking metal film can be used, whichmay be formed using chromium, molybdenum, nickel, titanium, cobalt,copper, tungsten, aluminum, or the like, for example.

There is no particular limitation on the formation method of thelight-blocking layer, and a dry method such as evaporation, sputtering,CVD, or the like or a wet method such as spin coating, dip coating,spray coating, droplet discharging (e.g., ink jetting), printing (e.g.,screen printing, or offset printing), or the like may be used dependingon a material used. If needed, an etching method (dry etching or wetetching) may be employed to form a desired pattern.

Further, the light-blocking layer can prevent light leakage to anadjacent pixel, which enables higher contrast and higher definitiondisplay.

In the display device illustrated in FIG. 1A, as the substrate 100,plastic (an organic resin), glass, quartz, or the like can be used. Asan example of plastic, a member made of polycarbonate, polyarylate,polyethersulfone, or the like can be given. Plastic is preferably usedfor the substrate 100, in which case a reduction in the weight of thedisplay device can be achieved. Alternatively, a sheet with a highbarrier property against water vapor and a high heat radiation property(e.g., a sheet including diamond like carbon (DLC)) can be used for thesubstrate 100.

Although not illustrated, a structure in which an inorganic insulator isprovided over the substrate 100 may be employed. The inorganic insulatorfunctions as a protective layer or a sealing film which blocks anexternal contaminant such as water. By providing the inorganicinsulator, deterioration of the light-emitting element can besuppressed; thus, the durability and lifetime of the display device canbe improved.

A single layer or a stack of a nitride film and a nitride oxide film canbe used as the inorganic insulator. Specifically, the inorganicinsulator can be formed using silicon oxide, silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride, orthe like by a CVD method, a sputtering method, or the like depending ona material used. Preferably, the inorganic insulator is formed usingsilicon nitride by a CVD method. The film thickness of the inorganicinsulator may be greater than or equal to 100 nm and less than or equalto 1 μm. Alternatively, an aluminum oxide film, a DLC film, a carbonfilm containing nitrogen, or a film containing zinc sulfide and siliconoxide (ZnS.SiO₂ film) may be used as the inorganic insulator.

Alternatively, a thin glass substrate can be used as the inorganicinsulator. For example, a glass substrate with a thickness greater thanor equal to 30 μm and less than or equal to 100 μm can be used.

A metal plate may be provided on a bottom surface of the substrate 100(a surface opposite to the surface over which the light-emitting elementis provided). In the case where an inorganic insulator is provided, ametal plate may be used instead of the substrate 100. Although there isno particular limitation on the thickness of the metal plate, a metalplate with a thickness greater than or equal to 10 μm and less than orequal to 200 μm is preferably used, in which case a reduction in theweight of the display device can be achieved. Further, although there isno particular limitation on the material of the metal plate, a metalsuch as aluminum, copper, or nickel, a metal alloy such as an aluminumalloy or stainless steel, or the like can be preferably used.

The metal plate and the substrate 100 can be bonded to each other withan adhesive layer. As the adhesive layer, a visible light curableadhesive, an ultraviolet curable adhesive, or a thermosetting adhesivecan be used. As examples of materials of such adhesives, an epoxy resin,an acrylic resin, a silicone resin, a phenol resin, and the like can begiven. A moisture-absorbing substance serving as a desiccant may becontained in the adhesive layer.

A metal plate has low moisture permeability; thus, by providing themetal plate, the entry of moisture into the light-emitting element canbe prevented. Consequently, by providing the metal plate, a highlyreliable display device in which deterioration due to moisture issuppressed can be provided.

Note that an inorganic insulating film may be formed to cover the firstlight-emitting element 132 a, the second light-emitting element 132 b,and the third light-emitting element 132 c. The inorganic insulatingfilm serves as a protective layer or a sealing film which blocks anexternal contaminant such as water. By providing the inorganicinsulating film, the deterioration of the light-emitting element can beinhibited; thus, the durability and lifetime of the display device canbe improved. A material similar to the material of the inorganicinsulator described above can be used as a material of the inorganicinsulating film.

A moisture-absorbing substance which serves as a desiccant may beprovided between the substrate 100 and the counter substrate 128. Themoisture-absorbing substance may be provided in a solid state such aspowdery state or may be provided in a state of a film containing amoisture-absorbing substance, over the first light-emitting element 132a, the second light-emitting element 132 b, and the third light-emittingelement 132 c by a film formation method such as a sputtering method.

A material similar to that of the substrate 100 can be used for thecounter substrate 128. The counter substrate 128 should have a propertyof transmitting visible light rays. In addition, a polarizing plate, anoptical film, or the like may be provided for the counter substrate 128.With use of the polarizing plate, the optical film, or the like,reflection of external light on the first pixel 130 a and the secondpixel 130 b can be prevented, which leads to improvement of thecontrast.

Alternatively, a color filter layer with high transmittance may beprovided for the first pixel 130 a and/or the second pixel 130 b, whichleads to improving the contrast as well as keeping low powerconsumption. FIG. 1B illustrates an example in which a color filterlayer with high transmittance is provided for each of the first pixel130 a and the second pixel 130 b in the display device illustrated inFIG. 1A. Note that most parts of the structure of the display deviceillustrated in FIG. 1B are common to those of the display deviceillustrated in FIG. 1A, and thus description of the common parts issometimes not given.

The display device illustrated in FIG. 1B includes a first pixel 230 a,a second pixel 230 b, and the third pixel 130 c. The first pixel 230 aincludes the first light-emitting element 132 a provided for thesubstrate 100 and a color filter layer 134 a provided in a regionoverlapping with the first light-emitting element 132 a in the countersubstrate 128. The second pixel 230 b includes the second light-emittingelement 132 b provided for the substrate 100 and a color filter layer134 b provided in a region overlapping with the second light-emittingelement 132 b in the counter substrate 128. The third pixel 130 cincludes the third light-emitting element 132 c provided for thesubstrate 100 and the color filter layer 134 c provided in a regionoverlapping with the third light-emitting element 132 c in the countersubstrate 128.

In FIG. 1B, the color filter layer 134 a preferably has a transmissioncenter wavelength in the blue wavelength region (for example, thetransmission center wavelength is 450 nm), because light emitted fromthe first light-emitting element 132 a can be output efficiently.

In general, a color filter layer with high transmittance of light in aparticular wavelength region easily transmits light in a wavelengthother than the particular wavelength region, and thus the color purityof light transmitted through the color filter layer may be decreased insome cases. For example, a color filter layer with high transmittance,which is a maximum transmittance of 80% or more in the blue wavelengthregion, has a maximum transmittance of 5% or more in the wavelengthregion of from 570 nm to 760 nm in some cases. In addition, a colorfilter layer with high transmittance, which is a maximum transmittanceof 75% or more in the green wavelength region, has a maximumtransmittance of 10% or more in the wavelength region of from 380 nm to450 nm in some cases. Accordingly, in order to inhibit reduction ofcolor purity, a color filter layer with relatively low transmittance ispreferably used.

However, the first light-emitting element 132 a used in the displaydevice in this embodiment is a light-emitting element with increasedcolor purity of blue light emitted from the first light-emitting layer,by adjusting an optical path length between the first reflectiveelectrode 102 a and the light-transmitting electrode 112 and utilizinginterference of light. Therefore, the intensity of light in regionsother than the blue wavelength region can be extremely lowered, and thushigh color purity can be maintained even when the color filter layer 134a with high transmittance of light in the blue wavelength region isused. For example, as the color filter layer 134 a, a color filter layerhaving a maximum transmittance of 80% or more in the blue wavelengthregion can be used. In this case, the color filter layer 134 a may havea maximum transmittance of 5% or more in the wavelength region of 570 nmto 760 nm. This is because visible light of 570 nm or more is weakenedby increasing the color purity of blue light from the firstlight-emitting layer with use of interference of light.

By applying the color filter layer 134 a with high transmittance in thismanner, light absorption by the color filter layer 134 a can be reduced,which leads to improvement of use efficiency of light. In addition, inorder that the transmittance of the color filter layer 134 a in the bluewavelength region can be 80% or more, for example, the concentration ofa coloring material contained may be low. Alternatively, the filmthickness of the color filter layer 134 a is decreased, and thereby,transmittance of light in the blue wavelength region may be increased.

In addition, in FIG. 1B, the color filter layer 134 b preferably has atransmission center wavelength in the green wavelength region (forexample, the transmission center wavelength is 550 nm), because lightemitted from the second light-emitting element 132 b can be outputefficiently.

Similarly to the first light-emitting element 132 a, the secondlight-emitting element 132 b is a light-emitting element with increasedcolor purity of green light emitted from the second light-emittinglayer, and thus, even when the color filter layer 134 b with hightransmittance of light in the green wavelength region is used, highcolor purity can be maintained. For example, as the color filter layer134 b, a color filter layer with a maximum transmittance of 75% or morein the green wavelength region can be used. In this case, the colorfilter layer 134 b may have a maximum transmittance of 10% or more inthe wavelength region of 380 nm to 450 nm. This is because visible lightof 450 nm or less is weakened by increasing the color purity of greenlight from the second light-emitting layer with use of interference oflight.

By applying the color filter layer 134 b with high transmittance oflight in the green wavelength region in this manner, light absorption bythe color filter layer 134 b can be reduced, which leads to improvementof use efficiency of light. In addition, with use of the color filterlayer 134 b, the color purity of the second pixel 230 b can be moreincreased, and thereby the color reproducibility of the display devicecan be improved.

In the example of FIG. 1B, the first pixel 230 a and the second pixel230 b are each provided with a color filter layer, but the embodiment ofthe present invention is not limited to the example, and either thefirst pixel 230 a or the second pixel 230 b, and the third pixel 130 cmay be provided with color filter layers. Note that the resonantwavelength of the second light-emitting element 132 b is longer thanthat of the first light-emitting element 132 a. Thus a possibility ofmixing colors of the second light-emitting element 132 b, caused by theresonant wavelength of light exhibiting green color and that of lightexhibiting blue color which are close to each other is higher than apossibility of mixing colors of the first light-emitting element 132 a.Therefore, it is very effective to provide the color filter layer 134 bin the second pixel 230 b for more favorable green chromaticity.

In addition, as the resonant wavelength of the light-emitting element isshorter, color mixing hardly occurs. For that reason, a pixel for lightwith a short wavelength is preferably provided with a color filter layerwith high transmittance. For example, the transmittance of light in theblue wavelength region of the color filter layer 134 a provided for thefirst pixel 230 a for blue (B) is preferably higher than that of thetransmittance light in the green wavelength region of the color filterlayer 134 b provided for the second pixel 230 b for green (G), and thetransmittance light in the green wavelength region of the color filterlayer 134 b provided for the second pixel 230 b for green (B) ispreferably higher than that of the transmittance of light in the redwavelength region of the color filter layer 134 c provided for the thirdpixel 130 c for red (R). The display device with such a structure canachieve both high color purity and low power consumption.

The display device illustrated in FIG. 1B can prevent reflection ofexternal light in the display portion and have an increased contrast byprovision of a color filter layer in each pixel. In addition, a colorfilter layer with high transmittance is provided for each of the firstpixel 230 a and the second pixel 230 b for emission color of light witha relatively short wavelength, and thus the display device can consumelow power as well as maintain color reproducibility.

FIG. 2 is a plane view illustrating an electrode structure in thedisplay portion in the display device of this embodiment. Note that inFIG. 2, for easy understanding, some parts (e.g., a second EL layer) ofcomponents are not illustrated. The display device in FIG. 2 is apassive matrix display device where the reflective electrodes 102 (thefirst reflective electrode 102 a, the second reflective electrode 102 b,and the third reflective electrode 102 c) provided in a stripe patternand the light-transmitting electrodes 112 (the first light-transmittingelectrode 112 a, the second light-transmitting electrode 112 b, and thethird light-transmitting electrode 112 c) provided in a stripe patternare stacked in a lattice pattern.

The EL layers included in the first light-emitting element 132 a, thesecond light-emitting element 132 b, and the third light-emittingelement 132 c are each continuous which is provided entirely between thereflective electrodes 102 and the light-transmitting electrodes 112.Therefore, the light-emitting elements are not needed to be formedseparately with use of metal masks, and a high-definition display devicecan be provided. For example, the horizontal definition can be 350 ppior more, preferably 400 ppi or more.

FIGS. 3A to 3C illustrate structural examples of light-emitting elementswhich can be applied to the display device in this embodiment.

A light-emitting element illustrated in FIG. 3A includes the reflectiveelectrode 102, the light-transmitting conductive layer 104, the first ELlayer 106, the charge-generation layer 108, the second EL layer 110, andthe light-transmitting electrode 112.

In the first light-emitting element 132 a, the second light-emittingelement 132 b, the third light-emitting element 132 c, the reflectiveelectrodes 102 (the first reflective electrode 102 a, the secondreflective electrode 102 b, and the third reflective electrode 102 c)are each provided on the side opposite to the direction where light isoutput and are each formed using a reflective material.

As such a reflective material, a metal material such as aluminum, gold,platinum, silver, nickel, tungsten, chromium, molybdenum, iron, cobalt,copper, or palladium can be used. In addition, any of the following canbe used: alloys containing aluminum (aluminum alloys) such as an alloyof aluminum and titanium, an alloy of aluminum and nickel, and an alloyof aluminum and neodymium; and an alloy containing silver such as analloy of silver and copper. An alloy of silver and copper is preferablebecause of its high heat resistance. Further, a metal film or a metaloxide film is stacked on and in contact with an aluminum alloy film,whereby oxidation of the aluminum alloy film can be prevented. Asexamples of a material for the metal film or the metal oxide film,titanium, titanium oxide, and the like are given. Further, the abovematerials are preferable, because they are present in large amounts inthe Earth's crust and inexpensive to achieve a reduction in the cost ofmanufacturing a light-emitting element.

In the example of this embodiment, the reflective electrodes 102 areused as the anodes of the light-emitting elements. However, theembodiment of the present invention is not limited to this structure.

The light-transmitting conductive layers 104 (the firstlight-transmitting conductive layer 104 a, the second light-transmittingconductive layer 104 b, and the third light-transmitting conductivelayer 104 c) are each formed using a material capable of transmittingvisible light as a single layer or a stacked-layer. For example, as sucha material having a light-transmitting property, indium oxide, indiumtin oxide, indium zinc oxide, zinc oxide, and zinc oxide to whichgallium is added, graphene, or the like can be used.

In addition, the light-transmitting conductive layers 104 can be formedwith the use of a conductive composition containing a conductive highmolecule (also referred to as a conductive polymer). As the conductivehigh molecule, a so-called π-electron conjugated conductive highmolecule can be used. For example, polyaniline or a derivative thereof,polypyrrole or a derivative thereof, polythiophene (PEDOT) or aderivative thereof, a copolymer of two or more kinds of aniline,pyrrole, and thiophene or a derivative thereof, and the like can begiven.

In the first light-emitting element 132 a, the second light-emittingelement 132 b, and the third light-emitting element 132 c, thereflective electrodes 102 and the light-transmitting conductive layers104 can each be processed into a desired shape by a photolithographyprocess and an etching process. Thus, a minute pattern can be formedwith good controllability, and thus a high-definition display device canbe provided.

In addition, the light-transmitting conductive layer 104 isindependently provided for each pixel, and thereby crosstalk can beprevented even when the film thickness of the light-transmittingconductive layer 104 is very large or the conductivity of thelight-transmitting conductive layer 104 is high.

The first EL layer 106 may include at least a light-emitting layer. Inthis embodiment, the first EL layer 106 includes the firstlight-emitting layer having a maximum emission peak in the bluewavelength region. In addition, the first EL layer 106 can have astacked structure in which a layer containing a substance having a highelectron-transport property, a layer containing a substance having ahigh hole-transport property, a layer containing a substance having ahigh hole-injection property, a layer containing a substance having ahigh electron-injection property, a layer containing a bipolar substance(a substance having a high electron-transport property and a highhole-transport property), and the like are combined as appropriate, inaddition to the light-emitting layer. A plurality of light-emittinglayers may be included.

For example, the first EL layer 106 may have a stacked-structure inwhich a hole-injection layer, a hole-transport layer, the firstlight-emitting layer, an electron-transport layer, and anelectron-injection layer are stacked. Needless to say, when thereflective electrode 102 is used as a cathode, the electron-injectionlayer, the electron-transport layer, the first light-emitting layer, thehole-transport layer, and the hole-injection layer may be stacked inthis order over the reflective electrode 102.

The hole-injection layer is a layer having a high hole-injectionproperty. As the substance having a high hole-injection property, forexample, metal oxides such as molybdenum oxide, titanium oxide, vanadiumoxide, rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide,hafnium oxide, tantalum oxide, silver oxide, tungsten oxide, andmanganese oxide can be used. A phthalocyanine-based compound such asphthalocyanine (abbreviation: H₂Pc), or copper(II) phthalocyanine(abbreviation: CuPc) can also be used.

Alternatively, the following aromatic amine compounds which are lowmolecular organic compounds can be used:4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), or the like.

Further alternatively, any of high molecular compounds (e.g., oligomers,dendrimers, or polymers) can be used. Examples of high molecularcompounds include poly(N-vinylcarbazole) (abbreviation: PVK),poly(4-vinyltriphenylamine) (abbreviation PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine (abbreviation:Poly-TPD). A high molecular compound to which acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS),or polyaniline/poly(styrenesulfonic acid) (PAni/PSS), can also be used.

In particular, for the hole-injection layer, a composite material inwhich an acceptor substance is mixed with an organic compound having ahigh hole-transport property is preferably used. With the use of thecomposite material in which an acceptor substance is added to asubstance having a high hole-transport property, excellent holeinjection from the anode can be obtained, which results in a reductionin the drive voltage of the light-emitting element. Such a compositematerial can be formed by co-evaporation of a substance having a highhole-transport property and a substance having an acceptor property. Thehole-injection layer is formed using the composite material, wherebyhole injection from the anode to the first EL layer 106 is facilitated.

As the organic compound for the composite material, various compoundssuch as aromatic amine compounds, carbazole derivatives, aromatichydrocarbon, and high molecular compounds (such as oligomer, dendrimer,and polymer) can be used. Such an organic compound used for thecomposite material is preferably an organic compound having a highhole-transport property. Specifically, a substance having a holemobility of 10⁻⁶ cm²/Vs or higher is preferably used. However, othersubstances than the above described materials may also be used as longas the substances have higher hole-transport properties thanelectron-transport properties. Such organic compounds which can be usedfor the composite material will be specifically shown below.

Examples of the organic compounds that can be used for the compositematerial include: aromatic amine compounds such as TDATA, MTDATA, DPAB,DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP);and carbazole derivatives such as 4,4′-di(N-carbazolyl)biphenyl(abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene(abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

In addition, it is possible to use the following aromatic hydrocarboncompounds: 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation:t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),9,10-bis[2-(1-naphthyl)phenyl)-2-tert-butylanthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, or the like.

Further alternatively, an aromatic hydrocarbon compound such as2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene,pentacene, coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi), or 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene(abbreviation: DPVPA) can be used.

Further, as an electron acceptor, organic compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) and chloranil; and transition metal oxides can be given. Inaddition, oxides of metals belonging to Groups 4 to 8 in the periodictable can be also given. Specifically, vanadium oxide, niobium oxide,tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,manganese oxide, and rhenium oxide are preferable since theirelectron-accepting properties are high. Among these, molybdenum oxide isespecially preferable since it is stable in the air and its hygroscopicproperty is low and is easily treated.

Note that the hole-injection layer may be formed using a compositematerial of a high molecular compound such as PVK, PVTPA, PTPDMA, orPoly-TPD and an electron acceptor described above.

In addition, when a layer containing a composite material describedabove is provided for the first EL layer 106, the optical path lengthmay be adjusted by controlling the film thickness of the layercontaining a composite material. In this case, the firstlight-transmitting conductive layer 104 a is not necessarily provided.

The hole-transport layer is a layer that contains a substance with ahigh hole-transport property. As the substance having a highhole-transport property, any of the following aromatic amine compoundscan be used, for example: NPB; TPD; BPAFLP;4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi); and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The substances mentioned here are mainly ones thathave a hole mobility of 10⁻⁶ cm²/V·s or higher. However, othersubstances than the above described materials may also be used as longas the substances have higher hole-transport properties thanelectron-transport properties. The layer containing a substance with ahigh hole-transport property is not limited to a single layer, and twoor more layers containing the aforementioned substances may be stacked.

For the hole-transport layer, a carbazole derivative such as CBP, CzPA,or PCzPA or an anthracene derivative such as t-BuDNA, DNA, or DPAnth maybe used.

Further alternatively, for the hole-transport layer, a high molecularcompound such as PVK, PVTPA, PTPDMA, or Poly-TPD can be used.

The first light-emitting layer is a layer containing a light-emittingorganic compound having a maximum emission peak in the blue wavelengthregion. As the light-emitting organic compound, for example, afluorescent compound which exhibits fluorescence or a phosphorescentcompound which exhibits phosphorescence can be used.

Examples of a fluorescent compound for blue that can be used for thefirst light-emitting layerN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA), and the like.

As examples of the phosphorescent compound for blue that can be used forthe first light-emitting layer, the following materials are given:bis[2-(4′,6′-difluorophenyl)pyridinato-N, C²′]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)), and the like.

Note that the first light-emitting layer may have a structure in whichthe above light-emitting organic compound (a guest material) isdispersed in another substance (a host material). As such a hostmaterial, various kinds of materials can be used, and it is preferableto use a substance which has a lowest unoccupied molecular orbital level(LUMO level) higher than the light-emitting substance and has a highestoccupied molecular orbital level (HOMO level) lower than that of thelight-emitting substance.

As specific examples of the host material that can be used for thelight-emitting element in this embodiment, the following are given:metal complexes such as tris(8-quinolinolato)aluminum(III)(abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(III)(abbreviation: Almq₃), bis(10-hydroxybenzo[h]quinolinato)beryllium(II)(abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen), andbathocuproine (BCP); condensed aromatic compounds such as9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (abbreviation: TPB3),9,10-diphenylanthracene (abbreviation: DPAnth), and6,12-dimethoxy-5,11-diphenylchrysene; aromatic amine compounds such asN,N-dipheyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA),N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA), NPB (or α-NPD), TPD, DFLDPBi, and BSPB; and thelike.

Alternatively, as the host material, plural kinds of materials can beused. For example, in order to suppress crystallization, a substancesuch as rubrene which can suppress crystallization, may be furtheradded. In addition, NPB, Alq, or the like may be further added in orderto efficiently transfer energy to the guest material.

When the structure in which a guest material is dispersed in a hostmaterial is employed, crystallization of the first light-emitting layercan be suppressed. Further, concentration quenching due to highconcentration of the guest material can be inhibited.

A high molecular compound can be used for the first light-emittinglayer. Specifically, as a light-emitting material which exhibits bluelight emission, the following can be used:poly(9,9-dioctylfluorene-2,7-diyl) (abbreviation: PFO),poly[(9,9-dioctylfluorene-2,7-diyl-co-(2,5-dimethoxybenzene-1,4-diyl)](abbreviation: PF-DMOP),poly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N′-di-(p-butylphenyl)-1,4-diaminobenzene]}(abbreviation:TAB-PFH), and the like.

The electron-transport layer is a layer that contains a substance with ahigh electron-transport property. As the substance having a highelectron-transport property, any of the following substances can beused, for example: a metal complex having a quinoline skeleton or abenzoquinoline skeleton such as tris(8-quinolinolato)aluminum(abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(abbreviation: Almq₃), bis(10-hydroxybenzo[h]-quinolinato)beryllium(abbreviation: BeBq₂), orbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). Alternatively, a metal complex or the like including anoxazole-based or thiazole-based ligand, such asbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂) orbis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂) canbe used. Besides the metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can also be used. Thesubstances mentioned here are mainly ones that have an electron mobilityof 10⁻⁶ cm²/V·s or higher. Furthermore, the electron-transport layer isnot limited to a single layer, and may have a stack structure of two ormore layers made of the aforementioned substances.

The electron-injection layer is a layer including a highelectron-injection substance. For the electron-injection layer, analkali metal, an alkaline-earth metal, or a compound thereof, such aslithium, cesium, calcium, lithium fluoride, cesium fluoride, calciumfluoride, or lithium oxide, can be used. In addition, a rare earth metalcompound such as erbium fluoride can also be used. Further, any of theabove substances which can form the electron-transport layer can beused.

The charge-generation layer 108 has a function of injecting holes to theEL layer on the cathode side and injecting electrons to the EL layer onthe anode side when a voltage is applied to the light-emitting elementand charges are generated.

The charge-generation layer 108 can be formed by using any of theabove-mentioned composite materials. Further, the charge-generationlayer 108 may have a stacked structure including a layer containing acomposite material and a layer containing another material. In thatcase, as the layer containing another material, a layer containing anelectron-donating substance and a substance with a highelectron-transport property, a layer formed of a transparent conductivefilm, or the like can be used. As for a light-emitting element havingsuch a structure, problems such as energy transfer and quenching hardlyoccur, and a light-emitting element which has both high light emissionefficiency and long lifetime can be easily obtained due to expansion inthe choice of materials. Moreover, a light-emitting element whichprovides phosphorescence from one of the EL layers and fluorescence fromthe other of the EL layers can be readily obtained.

When the charge-generation layer is arranged between the EL layersstacked as illustrated in FIG. 3A, the element can have high luminanceand a long lifetime while the current density is kept low. In addition,the voltage drop due to resistance of the electrode material can besuppressed, whereby uniform light emission in a large area is possible.

By adjustment of the film thickness of the charge-generation layer 108,it is also possible that the optical path length between the firstreflective electrode 102 a and the light-transmitting electrode 112 isadjusted. In this case, the first light-transmitting conductive layer104 a is not necessarily provided.

The second EL layer 110 may include at least a light-emitting layer. Inthis embodiment, the second EL layer 110 includes the secondlight-emitting layer having a maximum emission peak in the greenwavelength region and the third light-emitting layer having a maximumemission peak in the red wavelength region. In addition, the second ELlayer 110 can have a stacked structure in which a layer containing asubstance having a high hole-transport property, a layer containing asubstance having a high electron-transport property, a layer containinga substance having a high hole-injection property, a layer containing asubstance having a high electron-injection property, a layer containinga bipolar substance (a substance having high electron-transport and highhole-transport properties), and the like are combined as appropriate, inaddition to the light-emitting layer. In addition, the second EL layer110 may have a structure similar to the first EL layer 106 or a stackedstructure different from that of the first EL layer. For example, thesecond EL layer 110 may have a stacked structure in which ahole-injection layer, a hole-transport layer, the second light-emittinglayer, the third light-emitting layer, an electron-transport layer, anelectron-injection buffer layer, an electron-relay layer, and acomposite material layer in contact with the light-transmittingelectrode 112 are stacked. Note that the second EL layer 110 may havethree or more light-emitting layers.

The second light-emitting layer is a layer containing a light-emittingorganic compound having a maximum emission peak in the green wavelengthregion. As the light-emitting organic compound, for example, afluorescent compound which exhibits fluorescence or a phosphorescentcompound which exhibits phosphorescence can be used.

As a fluorescent compound for green light that can be used for thesecond light-emitting layer, the following can be given:N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracene-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), and the like.

Examples of such phosphorescent compounds for green light includetris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),bis[2-phenylpyridinato-N, C^(2′)]iridium(III)acetylacetonate(abbreviation: Ir(ppy)₂(acac)),bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate(abbreviation: Ir(pbi)₂(acac)),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation:Ir(bzq)₂(acac)), and tris(benzo[h]quinolinato)iridium(III)(abbreviation: Ir(bzq)₃).

Note that the second light-emitting layer may have a structure in whichthe above light-emitting organic compound (a guest material) isdispersed in another substance (a host material), similarly to the firstlight-emitting layer.

In addition, a high molecular compound can be used as the light-emittingorganic compound included in the second light-emitting layer.Specifically, as a light-emitting material which emits green light, thefollowing can be used: poly(p-phenylenevinylene) (abbreviation: PPV),poly[(9,9-dihexylfluorene-2,7-diyl)-alt-co-(benzo[2,1,3]thiadiazole-4,7-diyl)](abbreviation:PFBT),poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)],and the like.

The third light-emitting layer is a layer containing a light-emittingorganic compound that has a maximum emission peak in the red wavelengthregion. As the light-emitting organic compound, for example, afluorescent compound which exhibits fluorescence or a phosphorescentcompound which exhibits phosphorescence can be used.

As a fluorescent compound that emits red light, there areN,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD), and the like.

In addition, as examples of phosphorescent compounds that emit orangelight to red light, the following organometallic complexes are given:tris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation: Ir(pq)₃),bis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(pq)₂(acac)),(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)),(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)),bis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate(abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),(dipivaloylmethanato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(dpm)), and(2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine)platinum(II)(abbreviation: PtOEP).

Note that the third light-emitting layer may have a structure in which alight-emitting organic compound (a guest material) described above isdispersed in another substance (a host material), similarly to the firstlight-emitting layer and the second light-emitting layer.

In addition, a high molecular compound can be used as a light-emittingorganic compound included in the third light-emitting layer.Specifically, as a material for orange to red light emission, thefollowing can be used:poly[2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylenevinylene] (abbreviation:MEH-PPV), poly(3-butylthiophene-2,5-diyl) (abbreviation: R4-PAT),poly{[9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]},poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-bis(1-cyanovinylenephenylene)]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}(abbreviation: CN-PPV-DPD), and the like.

In the second EL layer 110, it is preferable to provide a compositematerial layer in contact with the light-transmitting electrode 112,because damages to the second EL layer 110 can be reduced especiallywhen the light-transmitting electrode 112 is formed by a sputteringmethod. The composite material layer can be formed using a compositematerial described above in which an acceptor substance is mixed with anorganic compound having a high hole-transport property.

Further, with use of an electron-injection buffer layer, an injectionbarrier between the composite material layer and the electron-transportlayer can be lowered; thus, electrons generated in the compositematerial layer can be easily injected into the electron-transport layer.

Any of the following substances having high electron injectionproperties can be used for the electron injection buffer layer: analkali metal, an alkaline earth metal, a rare earth metal, a compound ofsuch metal (including an alkali metal compound (e.g., an oxide such aslithium oxide, a halide, and carbonate such as lithium carbonate orcesium carbonate), an alkaline earth metal compound (including an oxide,a halide, and carbonate), a rare earth metal compound (including anoxide, a halide, and carbonate), and the like.

Further, in the case where the electron-injection buffer layer containsa substance having a high electron-transport property and a donorsubstance, the donor substance is preferably added so that the massratio of the donor substance to the substance having a highelectron-transport property ranges from 0.001:1 to 0.1:1. Note that asthe donor substance, an organic compound such as tetrathianaphthacene(abbreviation: TTN), nickelocene, or decamethylnickelocene can be usedas well as an alkali metal, an alkaline earth metal, a rare earth metal,a compound of such metal (e.g., an alkali metal compound (including anoxide of lithium oxide or the like, a halide, and carbonate such aslithium carbonate or cesium carbonate), an alkaline earth metal compound(including an oxide, a halide, and carbonate), and a rare earth metalcompound (including an oxide, a halide, and carbonate). Note that as thehighly electron-transport substance, a material similar to theabove-described materials for the electron-transport layer can be used.

Furthermore, an electron-relay layer is preferably formed between theelectron-injection buffer layer and the composite material layer. Theelectron-relay layer is not necessarily provided; however, by providingthe electron-relay layer having a high electron-transport property,electrons can be rapidly transported to the electron-injection bufferlayer.

The structure in which the electron-relay layer is sandwiched betweenthe composite material layer and the electron-injection buffer layer isa structure in which the acceptor substance contained in the compositematerial layer and the donor substance contained in theelectron-injection buffer layer are less likely to interact with eachother, and thus their functions hardly interfere with each other.Accordingly, an increase in the driving voltage can be prevented.

The electron-relay layer contains a substance having a highelectron-transport property and is formed such that the LUMO level ofthe substance having a high electron-transport property is locatedbetween the LUMO level of the acceptor substance contained in thecomposite material layer and the LUMO level of the substance having ahigh electron-transport property contained in the electron-transportlayer. In the case where the electron-relay layer contains a donorsubstance, the donor level of the donor substance is controlled so as tobe located between the LUMO level of the acceptor substance in thecomposite material layer and the LUMO level of the substance having ahigh electron-transport property contained in the electron-transportlayer. As a specific value of the energy level, the LUMO level of thesubstance having a high electron-transport property contained in theelectron-relay layer is preferably −5.0 eV or more, more preferably from−5.0 eV to −3.0 eV.

As the substance having a high electron-transport property contained inthe electron-relay layer, a phthalocyanine-based material or a metalcomplex having a metal-oxygen bond and an aromatic ligand is preferablyused.

As the phthalocyanine-based material contained in the electron-relaylayer, specifically, any of the followings is preferably used: CuPc,phthalocyanine tin(II) complex (SnPc), phthalocyanine zinc complex(ZnPc), cobalt(II) phthalocyanine, β-form (CoPc), phthalocyanine iron(FePc), and vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine(PhO-VOPc).

As the metal complex having a metal-oxygen bond and an aromatic ligand,which is contained in the electron-relay layer, a metal complex having ametal-oxygen double bond is preferably used. The metal-oxygen doublebond has acceptor properties (properties of easily accepting electrons);thus, electrons can be transferred (donated and accepted) more easily.Further, the metal complex which has a metal-oxygen double bond isconsidered stable. Thus, the use of the metal complex having themetal-oxygen double bond makes it possible to drive the light-emittingelement at low voltage more stably.

As a metal complex having a metal-oxygen bond and an aromatic ligand, aphthalocyanine-based material is preferable. Specifically, any ofvanadyl phthalocyanine (VOPc), a phthalocyanine tin(IV) oxide complex(SnOPc), and a phthalocyanine titanium oxide complex (TiOPc) ispreferable because a metal-oxygen double bond is more likely to act onanother molecular in terms of a molecular structure and an acceptorproperty is high.

Note that as the phthalocyanine-based materials described above, aphthalocyanine-based material having a phenoxy group is preferable.Specifically, a phthalocyanine derivative having a phenoxy group, suchas PhO-VOPc, is preferable. A phthalocyanine derivative having a phenoxygroup is soluble in a solvent. A phthalocyanine derivative having aphenoxy group is soluble in a solvent. For that reason, such aphthalocyanine derivative has an advantage of being easily handledduring formation of the light-emitting element and an advantage offacilitating maintenance of an apparatus used for forming a film.

The electron-relay layer may further contain a donor substance. Examplesof the donor substance include organic compounds such astetrathianaphthacene (abbreviation: TTN), nickelocene, anddecamethylnickelocene, in addition to an alkali metal, an alkaline earthmetal, a rare earth metal, and a compound of such metals (e.g., analkali metal compound (including an oxide such as lithium oxide, ahalide, and a carbonate such as lithium carbonate or cesium carbonate),an alkaline earth metal compound (including an oxide, a halide, and acarbonate), and a rare earth metal compound (including an oxide, ahalide, and a carbonate)). When such a donor substance is contained inthe electron-relay layer, electrons can be transferred easily and thelight-emitting element can be driven at lower voltage.

In the case where a donor substance is contained in the electron-relaylayer, in addition to the materials described above as the substancehaving a high electron-transport property, a substance having a LUMOlevel higher than the acceptor level of the acceptor substance containedin the composite material layer can be used. As a specific energy level,a LUMO level is −5.0 eV or more, preferably from −5.0 eV to −3.0 eV. Asexamples of such a substance, a perylene derivative and anitrogen-containing condensed aromatic compound, and the like can begiven. Note that a nitrogen-containing condensed aromatic compound ispreferably used for the electron-relay layer because of its stability.

As specific examples of the perylene derivative, the following can begiven: 3,4,9,10-perylenetetracarboxylicdianhydride (abbreviation:PTCDA), 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole(abbreviation: PTCBI), N,N′-dioctyl-3,4,9,10-perylenetetracarboxylicdiimide (abbreviation: PTCDI-C8H),N,N′-dihexyl-3,4,9,10-perylenetetracarboxylic diimide (Hex PTC), and thelike.

As specific examples of the nitrogen-containing condensed aromaticcompound, the following can be given:pirazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (abbreviation:PPDN), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene(abbreviation: HAT(CN)₆), 2,3-diphenylpyrido[2,3-b]pyrazine(abbreviation: 2PYPR), 2,3-bis(4-fluorophenyl)pyrido[2,3-b]pyrazine(abbreviation: F2PYPR), and the like.

Besides, 7,7,8,8-tetracyanoquinodimethane (abbreviation: TCNQ),1,4,5,8-naphthalenetetracarboxylicdianhydride (abbreviation: NTCDA),perfluoropentacene, copper hexadecafluoro phthalocyanine (abbreviation:F₁₆CuPc),N,N′-bis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl)-1,4,5,8-naphthalenetetracarboxylic diimide (abbreviation: NTCDI-C8F),3′,4′-dibutyl-5,5″-bis(dicyanomethylene)-5,5″-dihydro-2,2′:5′,2″-terthiophene (abbreviation: DCMT), methanofullerene (e.g.,[6,6]-phenyl C₆₁ butyric acid methyl ester), or the like can be used.

Note that in the case where a donor substance is contained in theelectron-relay layer, the electron-relay layer may be formed by a methodsuch as co-evaporation of a substance having a high electron-transportproperty and the donor substance.

The hole-injection layer, the hole-transport layer, and theelectron-transport layer may be each formed using any of theabove-described materials.

The light-transmitting electrode 112 is formed using alight-transmitting material because it is formed on the side where lightis output. As a light-transmitting material, indium oxide, indium tinoxide, indium zinc oxide, zinc oxide, zinc oxide to which gallium isadded, graphene, or the like can be used.

In addition, as the light-transmitting electrode 112, a metal materialsuch as gold, platinum, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, palladium, or titanium can be used. Alternatively, anitride of such a metal material (such as titanium nitride) or the likemay be used. In the case of using such a metal material (or a nitridethereof), the light-transmitting electrode 112 may be thinned so as tobe able to transmit light.

The element structure of a light-emitting element that can be applied tothe display device in this embodiment is not limited to that in FIG. 3A.For example, two light-emitting layers may be stacked in the first ELlayer 106, while one light-emitting layer may be formed in the second ELlayer. Alternatively, as illustrated in FIG. 3B, the light-transmittingconductive layer 104, the first EL layer 114 including the firstlight-emitting layer, a first charge-generation layer 108 a, the secondEL layer 116 including a second light-emitting layer, a secondcharge-generation layer 108 b, a third EL layer 118 including a thirdlight-emitting layer, and the light-transmitting electrode 112 may besequentially stacked over the reflective electrode 102.

Alternatively, as illustrated in FIG. 3C, the light-transmittingconductive layer 104, an EL layer 120 including a first light-emittinglayer 120 a, a second light-emitting layer 120 b, and a thirdlight-emitting layer 120 c, the light-transmitting electrode 112 may besequentially stacked over the reflective electrode 102. In addition, thelight-emitting layers between the reflective electrode 112 and thelight-transmitting electrode 102 may be stacked over the reflectiveelectrode 102 in the order of the longest wavelength to the shortestwavelength (in other words, light emitted from the light-emitting layerprovided on the reflective electrode 102 side has the longestwavelength).

The display device illustrated in this embodiment includes a pluralityof pixels that have a light-emitting element in each of which lightemitted from a light-emitting layer is resonated, between the reflectiveelectrode 102 and the light-transmitting electrode 112, and has no colorfilter layers in pixels for light with relatively short wavelengths (forexample, pixel for blue and/or pixel for green) or includes color filterlayers with high transmittance in pixels for light with relatively shortwavelengths (for example, pixel for blue and/or pixel for green) and acolor filter layer selectively in a pixel for light with a longwavelength (for example, pixel for red). By such a structure, a displaydevice that consumes less power, maintaining color reproducibility canbe provided.

The structures described in this embodiment can be used in appropriatecombination with any structure described in other embodiments.

Embodiment 2

In this embodiment, an active matrix display device that is oneembodiment of the present invention will be described with reference toFIGS. 4A and 4B. FIG. 4A is a plan view illustrating a display device.FIG. 4B is a cross-sectional view taken along the lines A-B and C-D inFIG. 4A

In the display device illustrated in FIGS. 4A and 4B, an elementsubstrate 410 and a sealing substrate 404 are attached to each otherwith a sealant 405, and a driver circuit portion (a source side drivercircuit 401 and a gate side driver circuit 403) and a pixel portion 402including a plurality of pixels are provided.

Note that a wiring 408 is a wiring for transmitting signals that are tobe inputted to the source side driver circuit 401 and the gate sidedriver circuit 403, and receives a video signal, a clock signal, a startsignal, a reset signal, and the like from a flexible printed circuit(FPC) 409 which serves as an external input terminal. Although only theFPC is illustrated here, a printed wiring board (PWB) may be attached tothe FPC. The display device in this specification includes not only adisplay device itself but also a display device to which an FPC or a PWBis attached.

The driver circuit portion (the source side driver circuit 401 and thegate side driver circuit 403) includes a plurality of transistors. Aplurality of pixels included in the pixel portion 402 each include aswitching transistor, a current controlling transistor, and a firstelectrode electrically connected to drain electrodes of the currentcontrolling transistor and the switching transistor.

Although the driver circuit portion (the source side driver circuit 401and the gate side driver circuit 403) and the pixel portion 402 areformed over the element substrate 410, FIG. 4B illustrates the sourceside driver circuit 401 which is included in the driver circuit portionand three pixels in the pixel portion 402.

The plurality of pixels in the pixel portion 402 include at least pixelsfor two colors. In this embodiment, an example is described in whichpixels for three colors, a red (R) pixel 420 a, a green (G) pixel 420 b,and a blue (B) pixel 420 c, are provided.

The pixels 420 a, 420 b, and 420 c respectively include light-emittingelements 418 a, 418 b, and 418 c and transistors 412 a, 412 b, and 412 cwhich are respectively electrically connected to the light-emittingelements 418 a, 418 b, and 418 c and function as switching transistors.In addition, the pixel 420 c includes a color filter layer 434 coverlapping with the light-emitting element 418 c.

The light-emitting elements 418 a, 418 b, and 418 c respectively includea stacked layer of a reflective electrode 413 a and a light-transmittingconductive layer 415 a, a stacked layer of a reflective electrode 413 band a light-transmitting conductive layer 415 b, and a stacked layer ofa reflective electrode 413 c and a light-transmitting conductive layer415 c. In addition, the light-emitting elements 418 a, 418 b, and 418 cinclude, over the respective stacked layers, a stacked layer of a firstEL layer 431 in which a first light-emitting layer is provided, acharge-generation layer 432, and a second EL layer 433 in which a secondlight-emitting layer and a third light-emitting layer are provided, anda light-transmitting electrode 417.

By adjusting the film thickness of each of the light-transmittingconductive layers 415 a, 415 b, and 415 c, in the pixel 420 a for blue(B), blue light emitted from the first light-emitting layer is resonatedbetween the reflective electrode 413 a and the light-transmittingelectrode 417; in the pixel 420 b for green (G), green light emittedfrom the second light-emitting layer is resonated between the reflectiveelectrode 413 b and the light-transmitting electrode 417; and in thepixel 420 c for red (R), red light emitted from the third light-emittinglayer is resonated between the reflective electrode 413 c and thelight-transmitting electrode 417.

In addition, as the color filter layer 434 c, a color filter layerhaving a transmission center wavelength in the red wavelength region canbe used.

In accordance with the emission color of light emitted from eachlight-emitting layer, the optical path length between the reflectiveelectrode and the light-transmitting electrode is optimized, andthereby, light of each color with high color purity can be output withhigh emission efficiency. In addition, by selective provision of thecolor filter layer 434 c only in the pixel for red (R), low powerconsumption and high color reproducibility of the display device can beachieved. In addition, light-emitting layers are formed with acontinuous film, instead of separately being formed in every pixel withuse of metal masks, which does not result in reduction in yield andprocess complication due to the use of the metal masks.

A CMOS circuit, which is a combination of an n-channel transistor 423and a p-channel transistor 424, is formed for the source side drivercircuit 401. The driver circuit may be any of a variety of circuitsformed with transistors, such as a CMOS circuit, a PMOS circuit, or anNMOS circuit. Although the example in which the source side drivercircuit and the gate side driver circuit are formed over a substrate isdescribed in this embodiment, one embodiment of the present invention isnot limited thereto. All or part of the source side driver circuit andthe gate side driver circuit may be formed outside a substrate, not overthe substrate.

Note that an insulator 414 is formed to cover end portions of thereflective electrodes 413 a, 413 b, and 413 c and end portions of thelight-transmitting conductive layers 415 a, 415 b, and 415 c.

In order to improve the coverage, the insulator 414 is provided suchthat either an upper end portion or a lower end portion of the insulator414 has a curved surface with a curvature. For example, when positivephotosensitive acrylic is used as a material for the insulator 414, onlyan upper end portion of the insulator 414 preferably has a curvedsurface with a radius of curvature (0.2 μm to 3 μm). For the insulator414, it is also possible to use either a negative type that becomesinsoluble in an etchant by light irradiation or a positive type thatbecomes soluble in an etchant by light irradiation. Here, the insulator414 is formed using a positive photosensitive acrylic resin film.

Materials of the color filter layer 434 c, the reflective electrodes 413a, 413 b, 413 c and the light-transmitting conductive layers 415 a, 415b, 415 c, the first EL layer 431, the charge-generation layer 432, thesecond EL layer 433, and the light-transmitting electrode 417 can be thematerials described in Embodiment 1.

The sealing substrate 404 is attached to the element substrate 410 withthe sealant 405; thus, light-emitting elements 418 (418 a, 418 b, and418 c) are provided in a space 407 enclosed by the element substrate410, the sealing substrate 404, and the sealant 405. Note that the space407 is filled with a filler and may be filled with an inert gas (e.g.,nitrogen or argon), an organic resin, or the sealant 405. A substancehaving a hygroscopic property may be used for the organic resin and thesealant 405.

Note that an epoxy-based resin is preferably used as the sealant 405. Itis preferable that such a material allows as little moisture and oxygenas possible to penetrate. As a material for the sealing substrate 404, aglass substrate, a quartz substrate, or a plastic substrate made offiberglass-reinforced plastics (FRP), polyvinyl fluoride (PVF),polyester, acrylic, or the like can be used.

As in this embodiment, an insulating film 411 which serves as a basefilm may be provided between the element substrate 410 and asemiconductor layer of the transistor. The insulating film has afunction of preventing diffusion of an impurity element from the elementsubstrate 410 and can be formed to have a single-layer structure or astacked-layer structure using one or more of a silicon nitride film, asilicon oxide film, a silicon nitride oxide film, and a siliconoxynitride film.

There is no particular limitation on the structure of the transistorwhich can be used in the display device disclosed in this specification;for example, a staggered type transistor or a planar type transistorhaving a top-gate structure or a bottom-gate structure can be used. Thetransistor may have a single-gate structure in which one channelformation region is formed, a double-gate structure in which two channelformation regions are formed, or a triple-gate structure in which threechannel formation regions are formed. Alternatively, the transistor mayhave a dual-gate structure including two gate electrode layerspositioned over and below a channel region with a gate insulating layertherebetween.

The gate electrode layers can be formed to have a single-layer orstacked-layer structure using a metal material such as molybdenum,titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, orscandium, or an alloy material containing any of these materials as itsmain component.

For example, as a two-layer structure of the gate electrode layer, thefollowing structures are preferable: a two-layer structure of analuminum layer and a molybdenum layer stacked thereover, a two-layerstructure of a copper layer and a molybdenum layer stacked thereover, atwo-layer structure of a copper layer and a titanium nitride layer or atantalum nitride layer stacked thereover, and a two-layer structure of atitanium nitride layer and a molybdenum layer. As a three-layerstructure, a three-layer structure in which a tungsten layer or atungsten nitride layer, an alloy layer of aluminum and silicon or analloy layer of aluminum and titanium, and a titanium nitride layer or atitanium layer are stacked is preferable.

The gate insulating layer can be formed to have a single-layer structureor a stacked-layer structure using a silicon oxide layer, a siliconnitride layer, a silicon oxynitride layer, and/or a silicon nitrideoxide layer by a plasma CVD method, a sputtering method, or the like.Alternatively, a silicon oxide layer formed by a CVD method using anorganosilane gas can be used as the gate insulating layer. As anorganosilane gas, a silicon-containing compound such astetraethoxysilane (TEOS) (chemical formula: Si(OC₂H₅)₄),tetramethylsilane (TMS) (chemical formula: Si(CH₃)₄),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (SiH(OC₂H₅)₃), ortrisdimethylaminosilane (SiH(N(CH₃)₂)₃) can be used.

A material of the semiconductor layer is not particularly limited andmay be determined as appropriate in accordance with the characteristicsneeded for the transistors 412 a, 412 b, 412 c, 423, and 424. Examplesof materials which can be used for the semiconductor layer will begiven.

As the material of the semiconductor layer, any of the following can beused: an amorphous semiconductor formed by a sputtering method or avapor-phase growth method using a semiconductor material gas typified bysilane or germane; a polycrystalline semiconductor formed bycrystallizing the amorphous semiconductor with the use of light energyor thermal energy; and a microcrystalline semiconductor. Thesemiconductor layer can be formed by a sputtering method, an LPCVDmethod, a plasma CVD method, or the like.

A single crystal semiconductor such as silicon or silicon carbide can beused for the semiconductor layer. When a single crystal semiconductor isused for the semiconductor layer, the size of the transistor can bereduced; thus, higher resolution pixels in a display portion can beobtained. In the case where a single crystal semiconductor is used forthe semiconductor layer, an SOI substrate in which a single crystalsemiconductor layer is provided can be used. Alternatively, asemiconductor substrate such as a silicon wafer may be used.

A typical example of an amorphous semiconductor is hydrogenatedamorphous silicon, and a typical example of a crystalline semiconductoris polysilicon and the like. Examples of polysilicon (polycrystallinesilicon) include so-called high-temperature polysilicon which containspolysilicon formed at a process temperature of 800° C. or higher as itsmain component, so-called low-temperature polysilicon which containspolysilicon formed at a process temperature of 600° C. or lower as itsmain component, and polysilicon obtained by crystallizing amorphoussilicon with the use of e.g., an element that promotes crystallization.Needless to say, a microcrystalline semiconductor or a semiconductorpartly containing a crystal phase can be used as described above.

Further, an oxide semiconductor may be used. As the oxide semiconductor,the following can be used: an oxide of four metal elements such as anIn—Sn—Ga—Zn—O-based oxide semiconductor; an oxide of three metalelements such as an In—Ga—Zn—O-based oxide semiconductor, anIn—Sn—Zn—O-based oxide semiconductor, an In—Al—Zn—O-based oxidesemiconductor, a Sn—Ga—Zn—O-based oxide semiconductor, anAl—Ga—Zn—O-based oxide semiconductor, or a Sn—Al—Zn—O-based oxidesemiconductor; or an oxide of two metal elements such as anIn—Zn—O-based oxide semiconductor, a Sn—Zn—O-based oxide semiconductor,an Al—Zn—O-based oxide semiconductor, a Zn—Mg—O-based oxidesemiconductor, a Sn—Mg—O-based oxide semiconductor, an In—Mg—O-basedoxide semiconductor, or In—Ga—O-based oxide semiconductor; an In—O-basedoxide semiconductor; a Sn—O-based oxide semiconductor; or a Zn—O-basedoxide semiconductor. Further, SiO₂ may be contained in the above oxidesemiconductor. Here, for example, an In—Ga—Zn—O-based oxidesemiconductor is an oxide containing at least In, Ga, and Zn, and thecomposition ratio of the elements is not particularly limited. TheIn—Ga—Zn—O-based oxide semiconductor may contain an element other thanIn, Ga, and Zn.

A thin film expressed by a chemical formula of InMO₃(ZnO)_(m) (m>0) canbe used for the oxide semiconductor layer. Here, M represents one ormore metal elements selected from Ga, Al, Mn, and Co. For example, M canbe Ga, Ga and Al, Ga and Mn, Ga and Co, or the like.

In the case where an In—Zn—O-based material is used as the oxidesemiconductor, the atomic ratio thereof is In/Zn=0.5 to 50, preferablyIn/Zn=1 to 20, further preferably In/Zn=1.5 to 15. When the atomic ratioof Zn is in the above preferred range, the field-effect mobility of atransistor can be improved. Here, when the atomic ratio of the compoundis In:Zn:O=X:Y:Z, the relation of Z>1.5X+Y is satisfied.

As the oxide semiconductor layer, an oxide semiconductor including acrystal with c-axis aligned (also referred to as a c-axis alignedcrystal (CAAC)), which is neither completely single crystal norcompletely amorphous, can be used.

As examples of materials for a wiring layer serving as a sourceelectrode layer or a drain electrode layer, the following are given: anelement selected from the group of Al, Cr, Ta, Ti, Mo, and W; an alloycontaining any of the above elements as its component; an alloy filmcontaining a combination of any of these elements; and the like. In thecase where heat treatment is performed, a conductive film preferably hasheat resistance high enough to withstand the heat treatment. Since theuse of Al alone brings disadvantages such as low heat resistance and atendency for corrosion, aluminum is used in combination with aconductive material having heat resistance. As such a conductivematerial having heat resistance, which is combined with Al, it ispossible to use an element selected from the group of titanium (Ti),tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr), neodymium(Nd), and scandium (Sc), an alloy containing any of these elements asits component, an alloy containing a combination of any of theseelements, or a nitride containing any of these elements as itscomponent.

An inorganic insulating film or an organic insulating film formed by adry method or a wet method can be used for an insulating film 419 whichcovers the transistors. For example, a silicon nitride film, a siliconoxide film, a silicon oxynitride film, an aluminum oxide film, atantalum oxide film, or a gallium oxide film which is formed by a CVDmethod, a sputtering method, or the like can be used. Alternatively, anorganic material such as polyimide, acrylic, benzocyclobutene,polyamide, or an epoxy resin can be used. Other than the above organicmaterials, a low-dielectric constant material (a low-k material), asiloxane-based resin, PSG (phosphosilicate glass), BPSG(borophosphosilicate glass), or the like can be used.

Note that the siloxane-based resin corresponds to a resin including aSi—O—Si bond formed using a siloxane-based material as a startingmaterial. The siloxane-based resin may include, as a substituent, anorganic group (e.g., an alkyl group or an aryl group) or a fluoro group.The organic group may include a fluoro group. A siloxane-based resin isapplied by a coating method and baked; thus, the insulating film 419 canbe formed.

Note that the insulating film 419 may be formed by stacking a pluralityof insulating films formed using some of the above-described materials.For example, a structure may be employed in which an organic resin filmis stacked over an inorganic insulating film.

In the above manner, the active matrix display device including thelight-emitting element in accordance with one embodiment of the presentinvention can be obtained.

Note that this embodiment can be freely combined with any of the otherembodiments.

Embodiment 3

In this embodiment, a display device that is capable ofthree-dimensional (3D) image display and uses the display device in anyof the above-described embodiments as its display panel will bedescribed with reference to drawings.

A display device illustrated in FIG. 5A includes a display panel 10 anda shutter panel 20 that is provided on the side where light is emittedfrom the display panel 10, that is, a side of the display device whichis viewed by a user. Note that the display device shown in FIG. 5Aincludes the display device in accordance with any of theabove-described embodiments as the display panel 10.

The shutter panel 20 includes a plurality of optical shutter regions.Each optical shutter region includes a liquid crystal element and aswitching element for selecting the transmissive or non-transmissivestate of the liquid crystal element. When the liquid crystal element isput in a non-transmissive state, light emitted from the display panel 10can be blocked.

By selectively providing a light-blocking region (barrier region) tolight emitted from the display panel 10, a particular viewing angle isgiven. Consequently, light is emitted to different space regions for aright-eye and a left-eye, so that a user recognizes only imagescorresponding to the respective eyes. Thus, the display device candisplay a 3D image. In other words, in FIG. 5A, the shutter panel 20serves as a so-called parallax barrier, and by providing the shutterpanel 20, a parallax is given to emission from the display panel andthus the display device can display a 3D image. When the light-blockingregion is not provided in the shutter panel 20 (when all the liquidcrystal elements included in the shutter panel 20 are brought into atransmissive state), a two-dimensional (2D) image can be displayed, and3D image display and 2D image display can be interchanged by switchingof the liquid crystal elements included in the shutter panel 20.

Note that a plurality of optical shutter regions included in the shutterpanel 20 can be driven either with active matrix driving in which aswitching element is provided for each of optical shutter regions in adot pattern, or with passive matrix driving in which a switching elementis provided for a plurality of optical shutter regions.

For electrodes of the liquid crystal elements, the electrode connectedto the switching element may be formed in stripe and the other may beformed in a plate shape to form optical shutter regions in a linepattern. The optical shutter regions can be formed in a dot pattern byusing a structure in which a pair of electrodes in stripes areoverlapped with each other in a lattice pattern with liquid crystalstherebetween, or a structure in which the electrodes connected to theswitching elements are formed in a dot pattern. Thus, a light-blockingregion or a light-transmitting region can be controlled more accurately.

By driving the optical shutter regions by the active matrix driving andseparately driving a plurality of pixels 130 included in the displaypanel 10 and the optical shutter regions included in the shutter panel20, both 3D image display and 2D image display can be achieved.

Although not illustrated in this embodiment, the shutter panel 20 isprovided with an optical film such as a polarizing plate, a retardationplate, or an anti-reflection film, or the like as appropriate. Theshutter panel 20 can employ a variety of transmissive liquid crystalelements and a variety of liquid crystal modes.

The display device in accordance with this embodiment is capable of 3Dimage display and 2D image display by separately controlling driving ofa plurality of pixel 130 included in the display panel 10 and driving ofa plurality of optical shutter regions included in the shutter panel 20.Here, drive frequency employed for the display panel 10 and drivefrequency employed for the shutter panel 20 are different. In otherwords, the display panel 10 should be constantly driven in order todisplay a moving image, and the shutter panel 20 should be regularly orirregularly driven in response to switching between 3D image display and2D image display. In that case, a period during which the shutter panel20 needs to be driven is much shorter than a period during which theshutter panel 20 is kept in a certain state.

The display device in FIG. 5A preferably further includes a controller30 for controlling the operation of the display panel 10 and shutterpanel 20. The controller 30 has a function of controlling movie displayin the display panel 10 and a function of making the shutter panel 20operate only in a desired period (hereinafter also referred to asoperation period) and retaining the state of the shutter panel 20 in aperiod other than the operation period (hereinafter also referred to asretention period). Providing the retention period for the operation ofthe shutter panel 20 can reduce the power consumption of the displaydevice.

FIG. 5B illustrates an example of an equivalent circuit diagram of theoptical shutter region. The optical shutter region can include atransistor 207, a liquid crystal element 206 to which a signal is inputthrough the transistor 207, and a capacitor 208 for holding thepotential of the signal. Whether light is transmitted or not is selectedby control of the alignment of liquid crystals in the liquid crystalelement 206 in response to the potential of the signal. Thus, in orderto perform such operation, it is necessary to hold the potential of thesignal for a long time. In order to meet the need, a channel region ofthe transistor 207 is preferably formed using an oxide semiconductor.This is because leakage of electric charge through the transistor 207can be inhibited, so that a fluctuation in the potential of the signalcan be suppressed.

An oxide semiconductor has a wider band gap and lower intrinsic carrierdensity than silicon. Thus, with the use of an oxide semiconductor forthe semiconductor layer of the transistor 207, a transistor that hasmuch smaller amount of off-state current than a transistor containing anormal semiconductor such as silicon or germanium can be formed. As theoxide semiconductor, any material described in Embodiment 2 can be used.

A transistor including a highly-purified oxide semiconductor hasextremely small off-state current. Specifically, the concentration ofhydrogen in the highly-purified oxide semiconductor that is measured bysecondary ion mass spectroscopy (SIMS) is 5×10¹⁹/cm³ or lower,preferably 5×10¹⁸/cm³ or lower, more preferably 5×10¹⁷/cm³ or lower,still more preferably 1×10¹⁶/cm³ or lower. In addition, the carrierdensity of the oxide semiconductor that can be measured by Hall effectmeasurement is lower than 1×10¹⁴/cm³, preferably lower than 1×10¹²/cm³,more preferably lower than 1×10¹¹/cm³. Further, the band gap of theoxide semiconductor is 2 eV or more, preferably 2.5 eV or more, morepreferably 3 eV or more.

Note that various experiments can show that off-state current of atransistor including such a highly-purified oxide semiconductor film asan active layer is small. For example, even in an element with a channelwidth of 1×10⁶ m and a channel length of 10 μm, in a range of 1 to 10 Vof voltage (drain voltage) between a source terminal and a drainterminal, off-state current can be lower than or equal to themeasurement limit of a semiconductor parameter analyzer, that is, lowerthan or equal to 1×10⁻¹³ A. In that case, it can be seen that off-statecurrent density corresponding to a value obtained by division of theoff-state current by the channel width of the transistor is lower thanor equal to 100 zA/μm (the unit A/μm corresponds to a current value permicrometer of a channel width).

Note that the concentration of hydrogen in a semiconductor film and aconductive film can be measured by secondary ion mass spectroscopy(SIMS). It is known that it is difficult to obtain precise data in thevicinity of a surface of a sample or in the vicinity of an interfacebetween stacked films formed using different materials by a SIMSanalysis in principle. Thus, in the case where the distribution of theconcentration of hydrogen in a film in a thickness direction is analyzedby SIMS, an average value in a region of the film in which the value isnot greatly changed and substantially the same value can be obtained isemployed as the hydrogen concentration. In addition, in the case wherethe thickness of the film is small, a region where substantially thesame value can be obtained cannot be found in some cases due to theinfluence of the hydrogen concentration in an adjacent film. In thatcase, the maximum value or the minimum value of the hydrogenconcentration in the region of the film is employed as the hydrogenconcentration of the film. Further, in the case where a mountain-shapedpeak having a maximum value or a valley-shaped peak having a minimumvalue do not exist in the region of the film, the value at an inflectionpoint is employed as the hydrogen concentration.

FIGS. 5C and 5D are flow charts each illustrating an operation exampleof the controller 30 in FIG. 5A. Specifically, FIG. 5C is a flow chartillustrating an operation example of the controller 30 for controllingthe display panel 10, and FIG. 5D is a flow chart illustrating anoperation example of the controller 30 for controlling the shutter panel20.

When the controller 30 starts to operate, a display control signal isoutput to the display panel 10 (see FIG. 5C). Here, the display controlsignal indicates image signals input to the plurality of pixels 130arranged in matrix, signals for controlling operation (e.g., clocksignals), and the like. The display control signal is constantlysupplied to the display panel 10 during display in the display panel 10is continued by the controller 30.

Further, in the case where the controller 30 operates and the displaydevice performs 3D image display, the controller 30 outputs alight-blocking control signal to the shutter panel 20 (see FIG. 5D).Here, the light-blocking control signal indicates control signals forthe transistor 207 (signals for determining light-blocking of the liquidcrystal element 206), signals for controlling operation (e.g., clocksignals), and the like. After control signals are supplied to thetransistor 207, supply of light-blocking control signals is stopped.Note that in the case where a region for 3D image display is changed,the controller 30 outputs a light-blocking control signal to the shutterpanel 20 again. In this manner, the light-blocking control signal isregularly or irregularly supplied to the shutter panel 20 when 3D imagedisplay is performed.

Note that in the flow chart in FIG. 5D, in the case where thelight-blocking control signal is not supplied to the shutter panel 20for a long time, a light-blocking control signal for performing 3D imagedisplay can be supplied to the shutter panel 20 again (refresh). Inother words, in the case where 3D image display is performed in thedisplay device for a long time, a light-blocking control signal forperforming 3D image display can be supplied to the shutter panel 20 asappropriate (regularly or irregularly).

As described above, the display device includes the display panel 10 andthe shutter panel 20 placed on the side where light is emitted from thedisplay pane; 10, and thus achieves 3D image display. Moreover, thedisplay device can display 3D images with high color reproducibility atlow power consumption when the display device described in any of theabove-described embodiments is used as a display panel. Further, a highdefinition 3D display can be performed.

The operation in this embodiment eliminates the need for constantlydriving the shutter panel 20, so that the power consumption of thedisplay device can be more reduced.

The methods, structures, and the like described in this embodiment canbe combined as appropriate with any of the methods and structuresdescribed in the other embodiments.

Embodiment 4

The display device in accordance with one embodiment of the presentinvention can be used for computers such as laptops, or imagereproducing devices provided with recording media (typically, deviceswhich reproduce the content of recording media such as digital versatilediscs (DVDs) and have displays for displaying the reproduced images).Other examples of electronic devices that can use the display device inaccordance with one embodiment of the present invention include cellularphones, portable game machines, personal digital assistants, e-bookreaders, cameras such as video cameras and digital still cameras,goggle-type displays (head mounted displays), navigation systems, audioreproducing devices (e.g., car audio systems and digital audio players),copiers, facsimiles, printers, multifunction printers, automated tellermachines (ATM), and vending machines. In this example, specific examplesof these electronic devices are described with reference to FIGS. 6A to6C.

FIG. 6A illustrates a portable game machine, which includes a housing5001, a housing 5002, a display portion 5003, a display portion 5004, amicrophone 5005, speakers 5006, an operation key 5007, a stylus 5008,and the like. The display device described in any of the above-describedembodiments can be used in the display portion 5003 or the displayportion 5004. It is possible to provide a portable game machine withhigh color reproducibility and low power consumption when the displaydevice described in any of the above-described embodiments is used asthe display portion 5003 or 5004. Note that although the portable gamemachine in FIG. 5A has the two display portions 5003 and 5004, thenumber of display portions included in the portable game machine is notlimited to two.

FIG. 6B illustrates a laptop computer, which includes a housing 5201, adisplay portion 5202, a keyboard 5203, a pointing device 5204, and thelike. The display device described in any of the above-describedembodiments can be used in the display portion 5202. It is possible toprovide a laptop computer with high color reproducibility and low powerconsumption when the display device described in any of theabove-described embodiments is used as the display portion 5202.

FIG. 6C illustrates a personal digital assistant, which includes ahousing 5401, a display portion 5402, operation keys 5403, and the like.The display device described in any of the above-described embodimentscan be used in the display portion 5402. It is possible to provide apersonal digital assistant with high color reproducibility and low powerconsumption when the display device described in any of theabove-described embodiments is used as the display portion 5402.

The methods, structure, and the like described in this embodiment can becombined as appropriate with any of the methods and structures describedin the other embodiments.

Example 1

In this example, measurement results of characteristics of a displaydevice in accordance with one embodiment of the present invention willbe described with reference to drawings and tables.

Fabrication methods of the light-emitting element R, the light-emittingelement G, and the light-emitting element B are described with referenceto FIG. 7. Shown below are structural formulae of organic compounds usedin this example (BPhen,9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), 9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation:CzPA), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP),N,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn),2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[/h]quinoxaline (abbreviation:2mDBTPDBq-II), 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBA1BP),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac)), and bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: Ir(tppr)₂(dpm))).

In each of the light-emitting element R, the light-emitting element G,and the light-emitting element B, an aluminum-titanium alloy film and atitanium film were formed sequentially by a sputtering method, to form afirst electrode 1101 over a substrate 1100 of glass. The film-thicknessand the area of the first electrode 1101 were 6 nm and 2 mm×2 mm,respectively. In this example, the first electrode 1101 was used as ananode.

Next, indium tin oxide containing silicon oxide was deposited over thefirst electrode 1101 by a sputtering method to form a first conductivelayer 1104 in each of the light-emitting element R and thelight-emitting element G. To obtain a microcavity effect in thelight-emitting element R, the light-emitting element G, and thelight-emitting element B, the film-thickness of the first conductivelayer 1104 in the light-emitting element R was 90 nm, the film-thicknessof the first conductive layer 1104 in the light-emitting element G was40 nm, and the first conductive layer 1104 was not provided in thelight-emitting element B.

Next, the substrate 1100 provided with the first electrode 1101 and thefirst conductive layer 1104 was fixed to a substrate holder in thevacuum evaporation apparatus so that a surface over which the firstelectrode 1101 and the first conductive layer 1104 were provided faceddownward. The pressure in the vacuum evaporation apparatus was reducedto about 10⁻⁴ Pa. Then, over the first electrode 1101 or the firstconductive layer 1104, PCzPA and molybdenum (VI) oxide wereco-evaporated to form a hole-injection layer 1111. The weight ratio ofPCzPA to molybdenum oxide was adjusted to 1:0.5 (=PCzPA:molybdenumoxide), and the film-thickness of the hole-injection layer 1111 was 20nm. Note that the co-evaporation method refers to an evaporation methodin which evaporation is carried out from a plurality of evaporationsources at the same time in one treatment chamber.

Next, over the hole-injection layer 1111, a 20-nm-thick PCzPA film wasformed to form a hole-transport layer 1112.

Over the hole-transport layer 1112, CzPA and 1,6mMemFLPAPrn wereco-evaporated so that the weight ratio of CzPA to 1,6mMemFLPAPrn was1:0.05 to form a light-emitting layer 1113. The film-thickness of thelight-emitting layer 1113 was 30 nm.

Over the light-emitting layer 1113, CzPA was deposited to a thickness of5 nm to form an electron-transport layer 1114 a.

Then, over the electron-transport layer 1114 a, a film ofbathophenanthroline (abbreviation: BPhen) was formed to a thickness of15 nm to form an electron-transport layer 1114 b.

A 1-nm-thick film of calcium (Ca) was deposited over theelectron-transport layer 1114 b by evaporation to form anelectron-injection layer 1115 a, and a 2-nm-thick film of copper(II)phthalocyanine (abbreviation: CuPc) was deposited over theelectron-injection layer 1115 a by evaporation to form anelectron-injection layer 1115 b.

Over the electron-injection layer 1115 b, PCzPA and molybdenum (VI)oxide were co-evaporated to form a charge-generation layer 1102. Theweight ratio of PCzPA to molybdenum oxide was adjusted to be 1:0.5(=PCzPA: molybdenum oxide). The thickness of the charge-generation layer1102 was 30 nm.

Over the charge-generation layer 1102, BPAFLP was deposited to athickness of 20 nm to form a hole-transport layer 1212.

Over the hole-transport layer 1212, 2mDBTPDBq-II, PCBA1BP, andIr(mppm)₂(acac) were co-evaporated so that the weight ratio of2mDBTPDBq-II to PCBA1BP and Ir(mppm)₂(acac) was 0.8:0.2:0.6 to form alight-emitting layer 1213. The thickness of the light-emitting layer1213 was 20 nm.

Over the light-emitting layer 1213, 2mDBTPDBq-II and Ir(tppr)₂(dpm) wereco-evaporated so that the weight ratio of 2mDBTPDBq-II to Ir(tppr)₂(dpm)was 1:0.02 to form a light-emitting layer 1313. The thickness of thelight-emitting layer 1313 was 20 nm.

Over the light-emitting layer 1313, 2mDBTPDBq-II was deposited to athickness of 15 nm to form an electron-transport layer 1214 a.

Over the electron-transport layer 1214 a, BPhen was deposited to athickness of 15 nm to form an electron-transport layer 1214 b.

Further, a lithium fluoride (LiF) film was formed to a thickness of 1 nmover the electron-transport layer 1214 b by evaporation, whereby anelectron-injection layer 1215 was formed.

Over the electron-injection layer 1215, silver and magnesium weredeposited to a thickness of 10 nm so that the volume ratio of silver tomagnesium was 10:1 to form a film containing silver and magnesium (AgMgfilm) as a second conductive layer 1105.

Over the second conductive layer 1105, indium tin oxide was deposited toa thickness of 50 nm by a sputtering method to form a second electrode1103.

Through the above steps, the light-emitting element R, thelight-emitting element G, and the light-emitting element B which wereused in this example were fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 1 shows the element structures of the light-emitting element R,the light-emitting element G, and the light-emitting element B whichwere fabricated in the above manner.

TABLE 1 first electrode first conductive hole-injection hole-transport1101 layer 1104 layer 1111 layer 1112 Light-emitting Al—Ti\Ti ITSOPCzPA:MoOx PCzPA element R 6 nm 90 nm (=1:0.5) 20 nm 20 nmLight-emitting Al—Ti\Ti ITSO PCzPA:MoOx PCzPA element G 6 nm 40 nm(=1:0.5) 20 nm 20 nm Light-emitting Al—Ti\Ti ITSO PCzPA:MoOx PCzPAelement B 6 nm  0 nm (=1:0.5) 20 nm 20 nm electron- electron-light-emitting transport layer injection layer charge-generation layer1113 1114a 1114b 1115a 1115b layer 1102 CzPA:1,6- CzPA BPhen Ca CuPcPCzPA:MoOx mMemFLPAPrn 5 nm 15 nm 1 nm 2 nm (=1:0.5) (=1:0.05) 30 nm 30nm CzPA:1,6- CzPA BPhen Ca CuPc PCzPA:MoOx mMemFLPAPrn 5 nm 15 nm 1 nm 2nm (=1:0.5) (=1:0.05) 30 nm 30 nm CzPA:1,6- CzPA BPhen Ca CuPcPCzPA:MoOx mMemFLPAPrn 5 nm 15 nm 1 nm 2 nm (=1:0.5) (=1:0.05) 30 nm 30nm hole-transport light-emitting light-emitting electron-transport layerlayer 1212 layer 1213 layer 1313 1214a 1214b BPAFLP 2mDBTPDBq 2mDBTPDBq2mDBTPDBq Bphen 20 nm II:PCBA1BP:Ir(mppm)₂acac II:Ir(tppr)₂dpm II 15 nm(=0.8:0.2:0.06) (=1:0.02) 15 nm 20 nm 20 nm BPAFLP 2mDBTPDBq 2mDBTPDBq2mDBTPDBq Bphen 20 nm II:PCBA1BP:Ir(mppm)₂acac II:Ir(tppr)₂dpm II 15 nm(=0.8:0.2:0.06) (=1:0.02) 15 nm 20 nm 20 nm BPAFLP 2mDBTPDBq 2mDBTPDBq2mDBTPDBq BPhen 20 nm II:PCBA1BP:Ir(mppm)₂acac II:Ir(tppr)₂dpm II 15 nm(=0.8:0.2:0.06) (=1:0.02) 15 nm 20 nm 20 nm electron-injection secondconductive second layer 1215 layer 1105 electrode 1103 LiF Ag:Mg ITO 1nm (=10:1) 50 nm 10 nm LiF Ag:Mg ITO 1 nm (=10:1) 50 nm 10 nm LiF Ag:MgITO 1 nm (=10:1) 50 nm 10 nm *The mixture ratios are all represented inweight ratios.

The light-emitting element R, the light-emitting element G, and thelight-emitting element B were sealed with a glass substrate in a glovebox under a nitrogen atmosphere so as not to be exposed to the air.Then, operation characteristics of these light-emitting elements weremeasured. Note that the measurement was carried out at room temperature(in an atmosphere kept at 25° C.).

FIG. 9 shows emission spectra of the light-emitting elements. In FIG. 9,the spectra of the light-emitting element R, the light-emitting elementG, and the light-emitting element B are shown by a thin solid line, athick solid line, and a thick dotted line, respectively, and thehorizontal axis represents wavelength (nm) and the vertical axisrepresents emission intensity (arbitrary unit).

In each of the light-emitting element R, the light-emitting element G,and the light-emitting element B, the optical path length between thefirst electrode 1101 serving as a reflective electrode and the secondelectrode 1103 serving as a light-transmitting electrode is adjusted toobtain a microcavity effect, and thus each desired spectrum is amplifiedso that the color purity can be high.

As illustrated in FIG. 9, in the light-emitting element R, favorable redlight emitted from the light-emitting layer 1313, which has a peakaround 607 nm, is observed. In the light-emitting element G, favorablegreen light emitted from the light-emitting layer 1213, which has a peakaround 538 nm, is observed. In the light-emitting element B, favorableblue light emitted from the light-emitting layer 1113, which has a peakaround 463 nm, is observed.

Next, the light-emitting element R, the light-emitting element G, andthe light-emitting element B were used to form a pixel R, a pixel G, anda pixel B, and a color filter layer CF(R), a color filter layer CF(G),and a color filter layer CF(B) were used to be overlapped with thelight-emitting element R, the light-emitting element G, and thelight-emitting element B, respectively to form a pixel RCF, a pixel GCF,and a pixel BCF.

The color filter layer CF(R), the color filter layer CF(G), and thecolor filter layer CF(B) were each formed in such a manner that CR-7001W(manufactured by FUJIFILM Corporation), CG-7001W (manufactured byFUJIFILM Corporation), and CB-7001W (manufactured by FUJIFILMCorporation) which were each used as a material was applied onto a glasssubstrate, and then baked at 220° C. for an hour. The thickness was 1.3μm to 1.4 μm. Note that the material for color filter layers was appliedonto the glass substrate by a spin coating method at a spinning rate of500 rpm for the color filter layer CF(R), 500 rpm for the color filterlayer CF(G), and at a spinning rate of 1000 rpm for the color filterlayer CF (B).

FIG. 10 shows the relation between wavelengths and transmittances of thecolor filter layer CF(R), the color filter layer CF(G), and the colorfilter layer CF(B). In FIG. 10, the rhombuses represent the color filterlayer CF(R), the squares represent the color filter layer CF(G) and thetriangles represent the color filter layer CF (B). The transmittance wasmeasured with U-4000 Spectrophotometer (manufactured by HitachiHigh-Technologies Corporation.) by setting light that is emitted from alight source and passes through the glass substrate to 100%.

The current efficiency, the CIE chromaticity coordinates (x, y), and thevoltage of each of the pixel R, the pixel GS the pixel B, the pixel RCF,the pixel GCF, and the pixel BCF were measured under the condition inwhich a luminance of about 1000 cd/m² was able to be obtained.

As for the pixel R, the current efficiency was 27 cd/A, the CIEchromaticity coordinates were (x, y)=(0.40, 0.31), and the voltage was6.4 V. As for the pixel G, the current efficiency was 55 cd/A, the CIEchromaticity coordinates were (x, y)=(0.38, 0.60), and the voltage was6.0 V. As for the pixel B, the current efficiency was 8.2 cd/A, the CIEchromaticity coordinates were (x, y)=(0.16, 0.16), and the voltage was7.6 V.

As for the pixel RCF, the current efficiency was 6.0 cd/A, the CIEchromaticity coordinates were (x, y)=(0.67, 0.32), and the voltage was7.0 V. As for the pixel GCF, the current efficiency was 33 cd/A, the CIEchromaticity coordinates were (x, y)=(0.31, 0.67), and the voltage was6.2 V. As for the pixel BCF, the current efficiency was 3.4 cd/A, theCIE chromaticity coordinates were (x, y)=(0.14, 0.10), and the voltagewas 8.4 V.

The chromaticities of the pixel R, the pixel G, the pixel B, the pixelRCF, the pixel GCF, and the pixel BCF are shown in the chromaticitycoordinates in FIG. 8. In FIG. 8, the black rhombus corresponds to thepixel R, the black square corresponds to the pixel G, the black trianglecorresponds to the pixel B, the white rhombus corresponds to the pixelRCF, the white square corresponds to the pixel GCF, the white trianglecorresponds to the pixel BCF and the solid line represents the NTSCratio defined by NTSC.

As shown in FIG. 8, the pixel B, the pixel BCF, the pixel G and thepixel GCF have less deviation from the NTSC ratio than the pixel R andthe pixel RCF, and thus are the pixel B and the pixel G, which are notprovided with color filter layers, have high color purity.

Next, with combination of the pixel R, the pixel G, the pixel B, thepixel RCF, the pixel GCF, and/or the pixel BCF, a reference displaydevice 1, a reference display device 2, a display device 1, and adisplay device 2 were manufactured, and NTSC ratios and powerconsumption for white emission were calculated. The pixel structures,NTSC ratios, and power consumption of the reference display device 1,the reference display device 2, the display device 1, and the displaydevice 2 are shown in Table 2.

TABLE 2 Pixels Power Red Green Blue NTSC consumption pixel pixel pixelratio (%) (a.u.) Reference RCF GCF BCF 84 1.00 display device 1 Displaydevice 1 RCF GCF B 76 0.80 Display device 2 RCF G B 60 0.66 Reference RG B 23 0.40 display device 2

The reference display device 1 includes the pixel RCF in the pixel forred, the pixel GCF in the pixel for green, and the pixel BCF in thepixel for blue, that is, all pixels have color filter layers, whichresults in high power consumption. In addition, the reference displaydevice 2 includes the pixel R in the pixel for red, the pixel G in thepixel for green, and the pixel B in the pixel for blue, that is, nocolor filter layers are provided in all pixels, which result in low NTSCratios.

On the contrary, the display device 1 in accordance with one embodimentof the present invention includes the pixel RCF in the pixel for red,the pixel GCF in the pixel for green, and the pixel B in the pixel forblue. That is, a color filter layer is provided only for each of thepixels for red and green, and thereby the color purity is increased andthe NTSC ratio is 76%, and no color filter layer is provided in thepixel for blue, and thereby power consumption is decreased to 0.80 ofthat of the reference display device 1. Similarly, the display device 2in accordance with another embodiment of the present invention includesthe pixel RCF in the pixel for red, the pixel G in the pixel for green,and the pixel B in the pixel for blue. That is, a color filter layer isprovided only for the pixel for red, and thereby the color purity isincreased and the NTSC ratio is 60%, and no color filter layers areprovided in the pixels for blue and green, and thereby power consumptionis decreased to 0.66 of that of the reference display device 1.

In addition, FIG. 11 shows the relation between wavelengths andtransmittances of the color filter layer CF(G) and color filter layerCF(B) with high transmittance. In FIG. 11, the thick line represents thecolor filter layer CF(G), and the thin line represents the color filterlayer CF(B). The transmittance was measured with U-4000Spectrophotometer (manufactured by Hitachi High-TechnologiesCorporation.) by setting light that is emitted from a light source andpasses through the glass substrate to 100%.

The color filter layer CF(G) and the color filter layer CF(B) in FIG. 11are color filter layers which are formed with the same material as thoseof the color filter layer CF(G) and the color filter layer CF(B)described above, and at a spinning rate of 1500 rpm or more for thecolor filter layer CF(G) and at a spinning rate of 2000 rpm or more forthe color filter layer CF(B) to be thinned for higher transmittance.

As shown in FIG. 11, the color filter layer CF(B) having a maximumtransmittance of 80% or more in the blue wavelength region has a maximumtransmittance of 5% or more in the wavelength region of 570 nm to 760nm. In addition, the color filter layer CF(G) having a maximumtransmittance of 75% or more in the green wavelength region has amaximum transmittance of 10% or more in the wavelength region of 380 nmto 450 nm.

The light-emitting element B used in the display device in this examplehas almost no spectra in the wavelength region of 570 nm or more asshown in FIG. 9. Therefore, the color filter layer CF(B) can be usedwithout any difficulty, even when the color filter layer CF(B) isthinned to obtain a maximum transmittance of 80% or more in the bluewavelength region and has a transmittance of 5% or more in thewavelength region of 570 nm to 760 nm.

Similarly, the light-emitting element G used in the display device inthis example has almost no spectra in the wavelength region of 450 nm orless as shown in FIG. 9. Therefore, the color filter layer CF(G) can beused without any difficulty, even when the color filter layer CF(G) isthinned to obtain a maximum transmittance of 75% or more in the greenwavelength region and has a transmittance of 10% or more in thewavelength region of 380 nm to 450 nm.

As described above, it can be known that, as in the display device 1 andthe display device 2 in accordance with embodiments of the presentinvention, a color filter layer is provided in at least only the pixelfor red and no color filter layers or color filter layers with hightransmittance are provided in the pixel for blue and the pixel forgreen, and thereby a display device with high color purity and low powerconsumption can be provided.

Example 2

In this example, an active matrix display device in accordance with oneembodiment of the present invention was manufactured and characteristicsthereof were measured. In this example, a display device in which nocolor filter layers are not provided in some pixels in accordance withone embodiment of the present invention (this device referred to asexample panel) and a display device in which color filter layers areprovided in all pixels (this device referred to as reference panel) weremanufactured and characteristics thereof were compared. The measurementresults are described below with reference to drawings and tables.

Structures of the example panel and the reference panel manufactured inthis example will now be described.

In the example panel, over a silicon substrate provided with atransistor such as a switching transistor or a driving transistor,pixels for R, G, and B with a display area with 3.93 inches in diagonal(79.92 mm×59.94 mm) were formed with a pixel density of 457.6 ppi with1440×1080 pixels.

The pixels used in the example panel are pixels having structuressimilar to the pixels described in Example 1. Specifically, pixelshaving structures similar to the pixel RCF, the pixel GCF, and the pixelB in Example 1 were used as the pixel for red (R), the pixel for green(G), and the pixel for blue (B), respectively.

In addition, the reference panel was also manufactured so as to have thesame size and pixel density as the example panel.

To the pixels used in the reference panel, light-emitting elementshaving different structures from those of the pixels in Example 1 wereapplied. The structures of the light-emitting elements used in thereference panel are described next.

The reference light-emitting elements used in the reference panel eachhave an electron-transport layer 1114 and an electron-injection layer1115 which are different from the electron-transport layer 1114 and theelectron-injection layer 1115 of the light-emitting element in Example1, but have the other layers similar to those of the light-emittingelement in Example 1. For that reason, the structures of only theelectron-transport layer and the electron-injection layer are describedin detail.

As the electron-transport layer 1114 of each reference light-emittingelement, a 15-nm-thick CzPA film was formed. As the electron-injectionlayer 1115 of each reference light-emitting element, a stacked layer ofan electron-injection layer 1115 a formed by co-evaporation of BPhen andCa (weight ratio of BPhen to Ca=1:0.04) and an electron-injection layer1115 b formed of a 2-nm-thick CuPc film was formed.

Table 3 shows the element structures of the reference light-emittingelements.

TABLE 3 First electrode First conductive Hole-injection Hole-transportLight-emitting 1101 layer 1104 layer 1111 layer 1112 layer 1113Reference Al—Ti\Ti ITSO PCzPA:MoOx PCzPA CzPA:1,6- light-emitting 6 nm90 nm (=1:0.5) 20 nm mMemFLPAPrn element R 20 nm (=1:0.05) 30 nmReference Al—Ti\Ti ITSO PCzPA:MoOx PCzPA CzPA:1,6- light-emitting 6 nm40 nm (=1:0.5) 20 nm mMemFLPAPrn element G 20 nm (=1:0.05) 30 nmReference Al—Ti\Ti ITSO PCzPA:MoOx PCzPA CzPA:1,6- light-emitting 6 nm 0 nm (=1:0.5) 20 nm mMemFLPAPrn element B 20 nm (=1:0.05) 30 nmElectron-transport Electron-injection layer Charge-generationHole-transport layer 1114 1115a 1115b layer 1102 layer 1212 CzPABphen:Ca CuPc PCzPA:MoOx BPAFLP 15 nm (=1:0.04) 2 nm (=1:0.5) 20 nm 5 nm30 nm CzPA Bphen:Ca CuPc PCzPA:MoOx BPAFLP 15 nm (=1:0.04) 2 nm (=1:0.5)20 nm 5 nm 30 nm CzPA Bphen:Ca CuPc PCzPA:MoOx BPAFLP 15 nm (=1:0.04) 2nm (=1:0.5) 20 nm 5 nm 30 nm Light-emitting Light-emittingElectron-transport layer Electron-injection layer 1213 layer 1313 1214a1214b layer 1215 2mDBTPDBq 2mDBTPDBq 2mDBTPDBq Bphen LiFII:PCBA1BP:Ir(mppm)₂acac II:Ir(tppr)₂dpm II 15 nm 1 nm (=0.8:0.2:0.06)(=1:0.02) 15 nm 20 nm 20 nm 2mDBTPDBq 2mDBTPDBq 2mDBTPDBq Bphen LiFII:PCBA1BP:Ir(mppm)₂acac II:Ir(tppr)₂dpm II 15 nm 1 nm (=0.8:0.2:0.06)(=1:0.02) 15 nm 20 nm 20 nm 2mDBTPDBq 2mDBTPDBq 2mDBTPDBq BPhen LiFII:PCBA1BP:Ir(mppm)₂acac II:Ir(tppr)₂dpm II 15 nm 1 nm (=0.8:0.2:0.06)(=1:0.02) 15 nm 20 nm 20 nm Second conductive Second layer 1105electrode 1103 Ag:Mg ITO (=10:1) 50 nm 10 nm Ag:Mg ITO (=10:1) 50 nm 10nm Ag:Mg ITO (=10:1) 50 nm 10 nm *The mixture ratios are all representedin weight ratios.

The reference panel was formed with use of the reference pixel RCF, thereference pixel GCF, and the reference pixel BCF in which color filterlayers were provided for the reference light-emitting element R, thereference light-emitting element G, and the reference light-emittingelement B having the above structures. Note that as the color filterlayers, ones similar to the color filter layers in Example 1 were used.

Characteristics of the example panel and the reference panelmanufactured in the above manner were measured. Note that thelight-emitting elements used in the reference panel are different fromthose used in the example panel, in the structures of theelectron-transport layers and the electron-injection layers; however,difference in emission characteristics and electric characteristics dueto that is small and thus the reference panel can be referred to, as acomparative example, without any difficulties.

FIGS. 12A and 12B show the chromaticity coordinates of the example paneland the reference panel. FIG. 12A shows the chromaticity coordinates ofthe reference panel, while FIG. 12B shows the chromaticity coordinatesof the example panel. In each of FIGS. 12A and 12 B, the pixel for red(R), the pixel for green (G), and the pixel for blue (B) in the panelare shown by the rhombus, the square, and the triangle, respectively,and white (W) color exhibited by the display panel is shown by the whitecircle. The solid lines show NTSC ratios.

The chromaticity coordinates of white color exhibited by the referencepanel are (x=0.30, y=0.37), and the chromaticity coordinates of whitecolor exhibited by the example panel are (x=0.31, y=0.30). In addition,NTSC ratios of the example panel and the reference panel are both 59%.Therefore, it is known that the example panel is a display panel thatcan exhibit color purity substantially the same as that of the referencepanel, even when not provided with a color filter layer in the B pixel.

Table 4 shows power consumption and NTSC ratios of the example panel andthe reference panel.

TABLE 4 Power consumption in lighting Pixels NTSC Total power rate RedGreen Blue ratio consumption of 20% pixel pixel pixel (%) (a.u.)equivalent Reference RCF GCF BCF 59 1.00 1.00 panel Example RCF GCF B 590.62 0.67 panel

The power consumption that is converted in a lighting rate of 20%equivalent described in Table 4 is a value obtained in the followingmanner: power consumption of pixels at a lighting rate of 20% isobtained first based on power (power consumption of the pixels) which isobtained by subtracting power consumption of a driver portion includinga switching transistor, a driver circuit, and the like, from the powerconsumption at the lighting rate 100% (the total power consumption), andthen, the power consumption of the driver portion is added to the powerconsumption of pixels at a lighting rate of 20%.

The example panel has no color filter layer in the pixel for blue, andthus the total power consumption of the example panel can be decreasedto 0.62 of that of the reference panel and is decreased to 0.67 even inthe lighting rate of 20% equivalent.

In addition, the example panel includes light-emitting elements thateach can resonate light emitted from the light-emitting layer betweenthe reflective electrode and the light-transmitting electrode and thuscan have increased color purities. For that reason, the NTSC ratiosubstantially the same as that of the reference panel in which colorfilter layers are provided in the all pixels can be obtained even whenno color filter layers are provided in some pixels (in this example, inthe pixel for blue light).

From the above results, the example panel manufactured in this examplecan have lowered power consumption as well as maintain colorreproducibility.

Reference Example

In this reference example, materials used in the light-emitting elementR, the light-emitting element G, and the light-emitting element B inExamples described above.

Synthesis Example of 1,6mMemFLPAPrn

In this example, an example is described in whichN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) used as the materials used in thelight-emitting element R, the light-emitting element G, and thelight-emitting element B is synthesized.

Step 1: Synthesis Method of3-methylphenyl-3-(9-phenyl-9H-fluoren-9-yl)phenylamine (Abbreviation:mMemFLPA)

In a 200 mL three-neck flask were put 3.2 g (8.1 mmol) of9-(3-bromophenyl)-9-phenylfluorene and 2.3 g (24.1 mmol) of sodiumtert-butoxide. The air in the flask was replaced with nitrogen. To thismixture were added 40.0 mL of toluene, 0.9 mL (8.3 mmol) of m-toluidine,and 0.2 mL of a 10% hexane solution of tri(tert-butyl)phosphine. Thetemperature of this mixture was set to 60° C., and 44.5 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture. Thetemperature of the mixture was set to 80° C., followed by stirring for2.0 hours. After the stirring, the mixture was suction-filtered throughFlorisil (produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135), Celite (produced by Wako Pure Chemical Industries, Ltd.,Catalog No. 531-16855), and alumina to give a filtrate. The filtrate wasconcentrated to give a solid, which was then purified by silica gelcolumn chromatography (the developing solvent has a 1:1 ratio of hexaneto toluene) and recrystallized with a mixed solvent of toluene andhexane. Accordingly, 2.8 g of the target substance, white solid, wasobtained in 82% yield. The synthesis scheme of this Step 1 is shown in(J-1).

[Step 2: Synthesis Method ofN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(Abbreviation: 1,6mMemFLPAPrn)]

In a 100 mL three-neck flask were put 0.6 g (1.7 mmol) of1,6-dibromopyrene, 1.4 g (3.4 mmol) of3-methylphenyl-3-(9-phenyl-9H-fluoren-9-yl)phenylamine, and 0.5 g (5.1mmol) of sodium tert-butoxide. The air in the flask was replaced withnitrogen. To this mixture were added 21.0 mL of toluene and 0.2 mL of a10% hexane solution of tri(tert-butyl)phosphine. The temperature of thismixture was set to 60° C., and 34.9 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture, and thismixture was set to 80° C., followed by stirring for 3.0 hours. After thestirring, 400 mL of toluene was added to the mixture, and the mixturewas heated. While the mixture was kept hot, it was suction-filteredthrough Florisil (produced by Wako Pure Chemical Industries, Ltd.,Catalog No. 540-00135), Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), and alumina to give afiltrate. The filtrate was concentrated to give a solid, which was thenpurified by silica gel column chromatography (the developing solvent hasa 3:2 ratio of hexane to toluene) to give a yellow solid.Recrystallization of the obtained yellow solid from a mixed solvent oftoluene and hexane gave 1.2 g of the target substance, yellow solid, in67% yield.

By a train sublimation method, 1.0 g of the obtained yellow solid waspurified. In the sublimation purification, the yellow solid was heatedat 317° C. under a pressure of 2.2 Pa with a flow rate of argon gas of5.0 mL/min. After the sublimation purification, 1.0 g of the targetsubstance, yellow solid, was obtained in a yield of 93%. The synthesisscheme of Step 2 is shown in (J-2).

A nuclear magnetic resonance (NMR) method identified this compound asN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn), which was the target substance.

¹H NMR data of the obtained compound is shown below.

¹H NMR (CDCl₃, 300 MHz): δ=2.21 (s, 6H), 6.67 (d, J=7.2 Hz, 2H), 6.74(d, J=7.2 Hz, 2H), 7.17-7.23 (m, 34H), 7.62 (d, J=7.8 Hz, 4H), 7.74 (d,J=7.8 Hz, 2H), 7.86 (d, J=9.0 Hz, 2H), 8.04 (d, J=8.7 Hz, 4H)

Synthesis Example of 2mDBTPDBq-II

A synthesis method of2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), which was used as the materials of the light-emittingelement R, the light-emitting element G, and the light-emitting elementB, will be described.

Synthesis of 2mDBTPDBq-II

A scheme for the synthesis of 2mDBTPDBq-II is shown in (C-1).

In a 2-L three-neck flask were put 5.3 g (20 mmol) of2-chlorodibenzo[f,h]quinoxaline, 6.1 g (20 mmol) of3-(dibenzothiophen-4-yl)phenylboronic acid, 460 mg (0.4 mmol) oftetrakis(triphenylphosphine)palladium(0), 300 mL of toluene, 20 mL ofethanol, and 20 mL of a 2M aqueous potassium carbonate solution. Themixture was degassed by being stirred under reduced pressure, and theatmosphere in the flask was substituted by nitrogen. This mixture wasstirred under a nitrogen stream at 100° C. for 7.5 hours. After cooledto room temperature, the obtained mixture was filtered to give a whitesubstance. The obtained substance by the filtration was washed withwater and ethanol in this order, and then dried. The obtained solid wasdissolved in about 600 mL of hot toluene, followed by suction filtrationthrough Celite (produced by Wako Pure Chemical Industries, Ltd., CatalogNo. 531-16855) and Florisil (produced by Wako Pure Chemical Industries,Ltd., Catalog No. 540-00135), whereby a clear colorless filtrate wasobtained. The obtained filtrate was concentrated and purified by silicagel column chromatography. The chromatography was carried out using hottoluene as a developing solvent. Acetone and ethanol were added to thesolid obtained here, followed by irradiation with ultrasonic waves.Then, the generated suspended solid was filtered and the obtained solidwas dried to give 7.85 g of the target substance, white powder, in 80%yield.

The above target substance was relatively soluble in hot toluene, but isa material that is easy to precipitate when cooled. Further, thesubstance was poorly soluble in other organic solvents such as acetoneand ethanol. Hence, the utilization of these different degrees ofsolubility resulted in a high-yield synthesis by such a simple method asabove. Specifically, after the reaction finished, the mixture wasreturned to room temperature and the precipitated solid was collected byfiltration, whereby most impurities were easily removed. Further, by thecolumn chromatography with hot toluene as a developing solvent, thetarget substance, which is easy to precipitate, was readily purified.

By a train sublimation method, 4.0 g of the obtained white powder waspurified. In the sublimation purification, the white powder was heatedat 300° C. under a pressure of 5.0 Pa with a flow rate of argon gas of 5mL/min. After the sublimation purification, 3.5 g of the targetsubstance, white powder, was obtained in a yield of 88%.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows:

¹H NMR (CDCl₃, 300 MHz): δ (ppm)=7.45-7.52 (m, 2H), 7.59-7.65 (m, 2H),7.71-7.91 (m, 7H), 8.20-8.25 (m, 2H), 8.41 (d, J=7.8 Hz, 1H), 8.65 (d,J=7.5 Hz, 2H), 8.77-8.78 (m, 1H), 9.23 (dd, J=7.2 Hz, 1.5 Hz, 1H), 9.42(dd, J=7.8 Hz, 1.5 Hz, 1H), 9.48 (s, 1H).

Synthesis Example of Ir(mppm)₂(acac)

A synthesis example of(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac)), which was used as the materials of thelight-emitting element R, the light-emitting element G, and thelight-emitting element B will be described.

Step 1: Synthesis of 4-methyl-6-phenylpyrimidine (Abbreviation: Hmppm)

First, in a recovery flask equipped with a reflux pipe were put 4.90 gof 4-chloro-6-methylpyrimidine, 4.80 g of phenylboronic acid, 4.03 g ofsodium carbonate, 0.16 g of bis(triphenylphosphine)palladium(II)dichloride (abbreviation: Pd(PPh₃)₂Cl₂), 20 mL of water, and 10 mL ofacetonitrile, and the air in the flask was replaced with argon. Thisreaction container was subjected to irradiation with microwaves (2.45GHz, 100W) for one hour to be heated. Here, in the flask were furtherput 2.28 g of phenylboronic acid, 2.02 g of sodium carbonate, 0.082 g ofPd(PPh₃)₂Cl₂, 5 mL of water, and 10 mL of acetonitrile, and the mixturewas heated again by irradiation with microwaves (2.45 GHz, 100 W) for 60minutes. After that, water was added to this solution and extractionwith dichloromethane was carried out. The obtained solution of theextract was washed with a saturated sodium carbonate aqueous solution,water, and then with saturated saline, and dried with magnesium sulfate.The solution which had been dried was filtered. The solvent of thissolution was distilled off, and then the obtained residue was purifiedby silica gel column chromatography using dichloromethane and ethylacetate as a developing solvent in a volume ratio of 9:1, so that apyrimidine derivative Hmppm, which was the target substance, wasobtained (orange oily substance, yield of 46%). Note that theirradiation with microwaves was performed using a microwave synthesissystem (Discover, manufactured by CEM Corporation). A synthesis scheme(b-1) of Step 1 is shown below.

[Step 2: Synthesis ofDi-μ-chloro-bis[bis(6-methyl-4-phenylpyrimidinato)iridium(III)](Abbreviation:[Ir(mppm)₂Cl]₂)]

Next, in a recovery flask equipped with a reflux pipe were put 15 mL of2-ethoxyethanol, 5 mL of water, 1.51 g of Hmppm obtained in Step 1above, and 1.26 g of iridium chloride hydrate (IrCl₃.H₂O), and the airin the flask was replaced with argon. After that, irradiation withmicrowaves (2.45 GHz, 100 W) was performed for 1 hour to cause areaction. The solvent was distilled off, and then the obtained residuewas washed with ethanol and filtered to give a dinuclear complex[Ir(mppm)₂Cl]₂ (dark green powder, yield of 77%). A synthesis scheme(b-2) of Step 2 is shown below.

Step 3: Synthesis of(Acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(Abbreviation: Ir(mppm)₂(acac))

Furthermore, into a recovery flask equipped with a reflux pipe were put40 mL of 2-ethoxyethanol, 1.84 g of the dinuclear complex [Ir(mppm)₂Cl]₂obtained in Step 2, 0.48 g of acetylacetone, and 1.73 g of sodiumcarbonate, and the air in the recovery flask was replaced with argon.Then, irradiation with microwaves (2.45 GHz, 100W) for 60 minutes wasperformed to cause reaction. The solvent was distilled off, the obtainedresidue was dissolved in dichloromethane, and filtration was performedto remove insoluble matter. The obtained filtrate was washed with waterand saturated saline, and was dried with magnesium sulfate. The solutionwhich had been dried was filtered. The solvent of this solution wasdistilled off, and then the obtained residue was purified by silica gelcolumn chromatography using dichloromethane and ethyl acetate as adeveloping solvent in a volume ratio of 4:1. After that,recrystallization was carried out with a mixed solvent ofdichloromethane and hexane to give the target substance, yellow powder(in 44% yield). A synthesis scheme (b-3) of Step 3 is shown below.

The result of nuclear magnetic resonance (¹H NMR) spectroscopy, by whichthe yellow powder obtained in Step 3 above was analyzed, is shown below.The result shows that this compound was(Acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac), which was the target substance.

¹NMR. δ (CDCl₃): 1.78 (s, 6H), 2.81 (s, 6H), 5.24 (s, 1H), 6.37 (d, 2H),6.77 (t, 2H), 6.85 (t, 2H), 7.61-7.63 (m, 4H), 8.97 (s, 2H).

This application is based on Japanese Patent Application serial no.2011-048230 filed with Japan Patent Office on Mar. 4, 2011, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A display device comprising: first to thirdlight-emitting elements each comprising: a first electrode; a firstlight-emitting layer over the first electrode; a charge-generation layerover the first light-emitting layer; a second light-emitting layer overthe charge-generation layer; and a second electrode over the secondlight-emitting layer; and a color filter layer overlapping with thefirst light-emitting element, the color filter layer having atransmission center wavelength in a red wavelength region, and wherein acolor filter layer overlapping with the second light-emitting element isnot provided, wherein a color filter layer overlapping with the thirdlight-emitting element is not provided, wherein a light emitted from thesecond light-emitting element has a maximum emission peak in a greenwavelength region, wherein a light emitted from the third light-emittingelement has a maximum emission peak in a blue wavelength region, whereinemission colors of the first and second light-emitting layers aredifferent from each other, and wherein an optical path length betweenthe first and second electrodes of the first light-emitting element, anoptical path length between the first and second electrodes of thesecond light-emitting element, and an optical path length between thefirst and second electrodes of the third light-emitting element aredifferent from each other.
 2. The display device according to claim 1,wherein the first and second light-emitting elements each comprises alight-transmitting conductive layer over the first electrode, wherein athickness of the light-transmitting conductive layer of the firstlight-emitting element and a thickness of the light-transmittingconductive layer of the second light-emitting element are different fromeach other.
 3. The display device according to claim 2, wherein thefirst light-emitting layer, the charge-generation layer, and the secondlight-emitting layer are each continuous between the first to thirdlight-emitting elements.
 4. The display device according to claim 1,wherein an area of the third light-emitting element is smaller than anarea of the first light-emitting element.
 5. The display deviceaccording to claim 1, wherein the first to third light-emitting elementseach comprises a layer including an organic compound between the firstand second electrodes, and wherein a thickness of the layer of the firstlight-emitting element, a thickness of the layer of the secondlight-emitting element, and a thickness of the layer of the thirdlight-emitting element are different from each other.
 6. The displaydevice according to claim 1, further comprising a substrate, wherein thefirst to third light-emitting elements are provided over the substrate.7. The display device according to claim 1, wherein a light emitted fromthe first light-emitting layer has shorter wavelength than a lightemitted from the second light-emitting layer.
 8. The display deviceaccording to claim 1, wherein the emission color of the firstlight-emitting layer is blue.
 9. A display device comprising: first tothird light-emitting elements each comprising: a first electrode; afirst light-emitting layer over the first electrode; a charge-generationlayer over the first light-emitting layer; a second light-emitting layerover the charge-generation layer; and a second electrode over the secondlight-emitting layer; and a color filter layer overlapping with thefirst light-emitting element, the color filter layer having atransmission center wavelength in a red wavelength region, and wherein acolor filter layer overlapping with the second light-emitting element isnot provided, wherein a color filter layer overlapping with the thirdlight-emitting element is not provided, wherein a light emitted from thesecond light-emitting element has a maximum emission peak in a greenwavelength region, wherein a light emitted from the third light-emittingelement has a maximum emission peak in a blue wavelength region, whereinemission colors of the first and second light-emitting layers aredifferent from each other, wherein fluorescence is provided from one ofthe first and second light-emitting layers, wherein phosphorescence isprovided from the other of the first and second light-emitting layers,and wherein an optical path length between the first and secondelectrodes of the first light-emitting element, an optical path lengthbetween the first and second electrodes of the second light-emittingelement, and an optical path length between the first and secondelectrodes of the third light-emitting element are different from eachother.
 10. The display device according to claim 9, wherein the firstand second light-emitting elements each comprises a light-transmittingconductive layer over the first electrode, wherein a thickness of thelight-transmitting conductive layer of the first light-emitting elementand a thickness of the light-transmitting conductive layer of the secondlight-emitting element are different from each other.
 11. The displaydevice according to claim 9, wherein an area of the third light-emittingelement is smaller than an area of the first light-emitting element. 12.The display device according to claim 9, wherein the first to thirdlight-emitting elements each comprises a layer including an organiccompound between the first and second electrodes, and wherein athickness of the layer of the first light-emitting element, a thicknessof the layer of the second light-emitting element, and a thickness ofthe layer of the third light-emitting element are different from eachother.
 13. The display device according to claim 9, further comprising asubstrate, wherein the first to third light-emitting elements areprovided over the substrate.
 14. The display device according to claim9, wherein the emission color of the first light-emitting layer is blue.15. The display device according to claim 9, wherein the firstlight-emitting layer, the charge-generation layer, and the secondlight-emitting layer are each continuous between the first to thirdlight-emitting elements.
 16. A display device comprising: first to thirdlight-emitting elements each comprising: a first electrode; a firstlight-emitting layer over the first electrode; a charge-generation layerover the first light-emitting layer; a second light-emitting layer overthe charge-generation layer; and a second electrode over the secondlight-emitting layer; and a color filter layer overlapping with thefirst light-emitting element, the color filter layer having atransmission center wavelength in a red wavelength region, and wherein acolor filter layer overlapping with the second light-emitting element isnot provided, wherein a color filter layer overlapping with the thirdlight-emitting element is not provided, wherein a light emitted from thesecond light-emitting element has a maximum emission peak in a greenwavelength region, wherein a light emitted from the third light-emittingelement has a maximum emission peak in a blue wavelength region, whereinemission colors of the first and second light-emitting layers aredifferent from each other, wherein a light emitted from the firstlight-emitting layer has shorter wavelength than a light emitted fromthe second light-emitting layer, and wherein an optical path lengthbetween the first and second electrodes of the first light-emittingelement, an optical path length between the first and second electrodesof the second light-emitting element, and an optical path length betweenthe first and second electrodes of the third light-emitting element aredifferent from each other.
 17. The display device according to claim 16,wherein a light emitted from the second light-emitting element has amaximum emission peak in a green wavelength region.
 18. The displaydevice according to claim 16, wherein the first and secondlight-emitting elements each comprises a light-transmitting conductivelayer over the first electrode, wherein a thickness of thelight-transmitting conductive layer of the first light-emitting elementand a thickness of the light-transmitting conductive layer of the secondlight-emitting element are different from each other.
 19. The displaydevice according to claim 16, wherein an area of the thirdlight-emitting element is smaller than an area of the firstlight-emitting element.
 20. The display device according to claim 16,wherein the first to third light-emitting elements each comprises alayer including an organic compound between the first and secondelectrodes, and wherein a thickness of the layer of the firstlight-emitting element, a thickness of the layer of the secondlight-emitting element, and a thickness of the layer of the thirdlight-emitting element are different from each other.
 21. The displaydevice according to claim 16, further comprising a substrate, whereinthe first to third light-emitting elements are provided over thesubstrate.
 22. The display device according to claim 16, wherein thefirst light-emitting layer, the charge-generation layer, and the secondlight-emitting layer are each continuous between the first to thirdlight-emitting elements.